Shadowhunter2077: I think they do it because it's easy for them to write them like this. In these fanfiction the opposite also happens to Percy and Annabeth: they no longer feel anything (fear, anger, love...) .
For Poseidon I have two hypotheses:
1) The first comes from Annabeth's speech to Percy in the book The sea of monsters in the chapter where they meet Circe: here Annabeth says: that the gods don't kill Percy because they are afraid of Poseidon. But I think Annabeth was referring to the fact that this could start a war (I could be wrong).
2) the second hypothesis is that Percy is powerful then Poseidon is powerful. But they don't consider the fact that Percy isn't that powerful, he needs other people to fight, for example HOO is based on this thing. I repeat I could be wrong if someone thinks differently from me say it.
Lipeghoul: I don't really like crossovers either, but there are some good crossovers.
Black Victor Cachat: It's a nice idea. But when it would be nice to have a fanfiction with adventures without the protagonists being modified too much.
TheFourthFate4Ever: where is it written? People are free to criticize. Sounds like for you I'm saying don't write these stories but that's not how, I'm just criticizing, people are free to read them or not to read my critiques.
TheNerdWithTheMythicalLaptop: That's very true.
Oof: Thanks for decreasing my years. How old am I for you? Tell me where did I go wrong? is where I wrote that people must think like me?
Today he criticizes her only for fanfiction where they make women weak, in every sense. They are warriors, their beauty comes from that, they don't need a male to live (I'm a male)