
Well, this kind of plot is aimed at horny teenagers, really. Besides, there isn't much of a plot, is there? So, what is the selling point?
Boobs and comedy.
Aren't boys just horny like that?
If you take a more serious manga, more in a genre like Seinen or even an Isekai like Saihate no Paladin, Goblin Slayer, Sousou no Frieren and such there is no ecchi and stuff, unless if necessary for the plot (Ex: Goblin slayer, when the woman are to be/are raped by the goblins. They can't be raped with their panties on).
Yes, I, too, would like a silly Isekai with a male protagonist with no Ecchi nor Harem involved, but since the plot is silly, unless if the plot itself and characters constructions is good, it is needed.
Such an example would be...well, sorry, forgot the name. A merchant and another guy who were summoneed to another world; He got married to a beast woman and stayed faithful to her. There is only one sex scene and it is only implicit they had sex. Nothing more, nothing less. You don't see her undressed and nothing like that.
But in this one the difference is that, altho being quite silly, you are drawn to the protagonist and his wife. The other guy summoned is such a retard and together with the boobies girl (no boobies pic) they look like team rocket, really.
So, it is a fun manga to read.
Another one would be one that, up until now, no females have appeared so far. A noble was suddenly in another world. There, he hires an adventure for some time but ends up becoming friends with him.
It draws attention because although not explicit, it gives you a shounen ai vibe (the author said it is not).
And there are many more. (ok, that I know of only 3 or 4)
Sorry for this being so long. Shortening it, this kind of plot is just so overused and sometimes written by amateurs (most of them are based in web novels, then became novels, then manga) who just wrote whatever their heart desired, not thinking about the plot itself but more of what they want.
Some are already works of professionals.
It just depends on where you look, really.

Exactly, exactly, exactly!!!
I'm not fan of harem, but I have some harem mangas that are my favorite because it is not the tipical mindless harem that we see in almost 90% of harem mangas (I'm not counting reverse harem)!
Even Reverse Haren is getting annoying. I remember when fan service began to appear it was funny, now it is only show naked bodies every two pages!!!
And the one I hate the most are the pedo fan service and pedo harem!!! Many think it is ok if it is the minor that get naked herself, ask sex but the guy says no!!!
There were some mangas with good plot until they decided to add fan service and harem changing even the personality of the female characters to become the midless horny woman that only wants MC pennis, and in one the MC, even though his mind is an adult, has sex with a women while he is a kid (has a kid body)!
So yeap... mindless plots and the want to attract more readers has ruin harem and even reverse harem!

Glad to find someone like-minded about this subject!
Yeah, reverse harem is funny in situations like Bakarina, where you just love the protagonist. When the protago is just that frail, flower like girl it is just...bleeehhh
Pedo fan service should give you jail time, honestly speaking. If I am reading a manga and a pedo fan service appears...first comes disgust, then I close the tab and go clean my eyes with dog/cat/cute animals pics. This is something that is becoming kind of "normal" and "accepted" for some reason. Shouldn't it be the other way around? Shouldn't it be becoming more and more non-acceptable? I hate it when there is a pedo guy, but it's like "since he is so funny, isn't it fine?" No! Arrest that character and don't let him out again! What makes me even madder is when the pedo is a woman and it is acceptable because she is a woman! Pedo is pedo, independently of your sex!
Yeah, sometimes the plot is good and then fan service comes. There are manga that they are starting to mix hentai with shounen. The other day I read the raws of one Isekai and holy cow, it became a low key hentai.
I say low key, but even hentai manga usually censor the boobs. That one did not.
Isekai is a genre usually aimed at young teens; Perhaps discovering their sexuality and being horny and stuff. So to the editors and mangaka it's like "It's fine", but don't they think about the younger kids who are drawn to this and go read it? Children read this kind of stuff.
Children.
It's not like parents supervision can stop it; There's school for that; To dirty your mind.
So yeah...I don't know what the heck is happening here, but I think things are going backwards, and not forwards.

Almost everyone that defend pedo fan service and pedo harem says the same thibg: tge guy try so hard do not touch them or see another way because he doesn't want to be a lolita...
First: the bad thing is sexualizing a minor, even if she is draw
Second: the ML is openly turned on by the minors but because his repitation he avoid the girls
Many isekais try to justify it with "in that world is something that happen" that is why the girls see normal offering their bodies to the ML!!!
There is also " the girl is a reincarnation of an adult woman" so is not pedo fan service because the girl is technically an adult (that was also ghe justification they gave me when I was shocked about the boy having sex with an adult woman)...
And sadly those justication have been told to me from men and women, maby of them see the pedo fans service and harem as something so normal that is scary!
Sigh... even hardcore harem lovers are getting annoyed about harem!

Another sad part is that it isn't just in the manga world, but in the real world as well. Movies, tv shows and etc. Some do sexualize children to some extent; In the past they did it much more, but they still do it nowadays.
When I was a child those children movies with a pretty Teen who would use some sexy clothing, the actresses were full fledged adults over 30. Nowadays they are...teens. Real teens playing the role of a teen using...little clothing.
What about that girl who is not even 13 who was selected as the sexiest woman in the world a few years back?
I think that worse than that "the girl is a reincarnation of an adult woman" is when a child gets the body of an adult and they start sexualizing her in these manga. Her mind still is that of a child.
She is a child.
I am aware that the sexualization in these manga are pure fiction, but it does stimulate people who are dangerous to society. It does give an opening for the younger teenagers to start thinking that "It is fine" since their minds are still in the growing process; They don't have fully formed opinions of their own.
Sometimes I feel like these manga and movies are kind of sending a seriously wrong message. And sadly, some people convey these to real life instead of letting it be in this fiction world. Then come the trolls who just put fuel into the fire and gets even worse.
I guess the world is moved purely and solely by money; Even if the cost is sexualizing children in a fictional way.
Wtf ik there isn’t an ecchi tag but I should’ve expected it considering how all the female characters have fucking massive boobs :(( and all stories like this end up being some fucking huge haram. Anyways disappointed and idk if I’m gonna continue reading lol