I hate A LOT of things in recent novel and manga trend, but I think I can boil it down to one thing and one thing only: Emotionally Distant self-insert.
Imagine this. A 20-or-so old guy died and reincarnated as a child of loving parents, and he pretends he's a child in front of them and his friends. And I don't mean, "I have memories of my past life even though I'm mentally a child," I mean a full-grown-ass adult with fully matured mind with all of his memory intact. The kind that is basically an adult in every way except his age. Yeah, that's creepy. That's manipulative. These people genuinely love him, they care for him, they give their heart, body, and soul for him, but he lies to them without even sparing a single thought. For what reason? You can't defend this kind of character without making them sound emotionally distant from their own parents. The authors don't want them to be vulnerable, since these characters are self-insert, they just want to be loved unconditionally. "There HAS to be a world where people love me even if I constantly lie to them, right?" Although, I think the author forgot that you can't expect people to genuinely love you if you're not being genuine with them back.
Just tell them, man. If they love you and you love them back, then be vulnerable around them. It hurts being lied to.
This applies with almost everything I have beef with. Super OP abilities? It's just an excuse for the self-insert to be different than the rest of the cast. Same with why there's rarely any decent character other than the self-insert protagonist. "I don't want to have an equal, I want to be unique, I want to be the top of everything." But the authors will never say it out loud, heck, they will even outright deny it at times. Why? Because that's a vulnerability. Saying it will make the author emotionally vulnerable. That's also the reason why slave girls are such a common trope. I mean, come on, you can have a girl with you all the time without any deeper reason than money? "oh, but I saved her so even if she's a slave I never actually used money" Yeah but she is still a slave and you're just making excuses. The author could make her anything but a slave, they just want an excuse not to be emotionally invested. Even garden variety, black hair black cloak, blander than slice of bread, plain main characters. They're literally just stolen asset, there's no shred of author's own characteristics in them.
It is the fear of being genuine that is plaguing the mainstream novel and manga, heck, even the entire internet, that makes these stories so bad. Authors no longer put themselves out, they hide behind layers of "intellectual" difference (which, with Japanese authors, unfortunately doesn't amount much) between one story and another. This is why we keep seeing copy paste of every isekai ever that has ever existed ever. These stories just don't have heart anymore.
Also, who the hell ever decided that getting reincarnated means receiving a cheat-like ability? That thing has become such a big trope in Japanese web novel scene that newer novels actually subvert that trope by making the protagonist "not" getting cheat-like abilities after questioning the "God/Goddess." Also, also, as a believer, I hate how Japanese authors think they know everything about God and religion and afterlife, even though their only knowledge of things of such nature is based on other shitty isekai.
