It's because Dialovers anime was mainly made for adv of the game, they couldn't make an harem ending (lol) but they showed some parts of each ones route.
THAT, as someone who played the game, was pretty clear.
So as frustrating as it is that Yui didn't end up with the boy you wanted, you can change that in the game (๑•ㅂ•)و✧
Hope I could explain it a little?
As this is a manga, sensei shows us the mainly possible couples, with different people, so I think most of 'em will be cannon ~ ヾ(❀╹◡╹)ﾉ~
There's a different in simulation games and such. Games like that has multiple endings and you can end up with anybody and still get a true ending.
Where yarichin is not just basically looking at only Toono POV, but all the characters of POV, like Tamura, Fujisaki, Itome, or somewhat somewhat,
The protagonist of Diabolik Lovers was a total masochist who barely did anything or speak up for herself imo (in my opinion). She's very bland and submissive. Toono isn't at all
I understand this is a video game but what if this manga turns out like diabolic lovers?!? Where you think there will be cannon but no one ends up with anyone? I’m pretty sure I’m wrong but I just thought of that show