Why does everyone, except MC and dude that died, suck?

Because it's a toxic bl and that's a possibility in toxic BLs lmao

Usually there’s at least 3-5 likeable characters that are alive in toxic BLs I guess this one just said fuck it

I mean it all depends on how you define likeable, I personally like everyone except the dad and the girl with purple hair

I think what you mean to say is "morally virtuous" characters. Because usually in toxic BL the only people who are truly disliked are the ones ruining the main relationship, or an uncharismatic rival.