
If you watched the last current chapter (19) and correlate it with how the current king likes his regasses, you'll be able to pinpoint that going forward from abel's death, the corrupt officers will pick regasses with the same build as the current Abel, to trap the prince further. So picking a completely different future "reincarnated Abel" is essential to the story. Not only that it'll disrupt the "associating" method used to control the prince, it'll also leave us with "don't judge the book by it's cover" as was experienced by current abel with his burly build and the prince with his root. Author's message here is pretty deep and crucial to the moral lesson picked, so old don't ruin it with such complains

Dude , let people complain. No one is ruining anything lol
No one is obligated to like every choice the authors make.
The author came up with a way so they could make their appearance uke like. That's the reason.
If they didn't want they certainly wouldn't go around to make them look how a lot of ukes looks. They wrote and they decided to got this route. It's not deep, it's an artistic and personal choice. And people can dislike that or like it.
It's not uncommon for bl to do this lol
Mdzs, At the End of the Road, Fall In Mistaken Love, Two empires : a tale of one slave, Kill the lights, Akuma wa Tengoku ni Ikitakunai, The Time a Gangster was Reincarnated as Ranmaru Mori, To be or not to be and those the bottoms were regarded as masculines, there a bunch where the mc is just normal looking but became very uke like after they died or isekaied lol. For you who Grieves, Monochrome Factor, The Perfect Prince Loves Me, His Rival?! etc.

Oh hey !
These ones, i purposely look it up those i remembered who fit the description of change of masculine to bishounenedfied body, if that's okay with you
Reincarnated Into Demon King Evelogia's World is great and breaks the stereotype, I became the lousy top is funny too, i can see your Stats, See you My King, Who is spying, I have to became a great villain ... And there is an author who publishes for free on t/ Apa /s their trilogy isekai project : the first is Change your path and second and current ongoing Second Chance-First World.
You can easily find more titles looking up tags like isekai bl, reeincarnation bl list etc too ! There is a toon! Or look it up transmigration bl too.
why you must make abel reincarnated as a twink, I like the way he is now