Why everybody hates Peugeot Citroen and Seat?

Not everybody and not just those three.

Dont trust everybody, check figures.

While they may not exactly be reliability champions, there are many successful and reliable models among the three. Some have had problems, like all the rest, up to Mercedes and beyond. The only group that has performed consistently for decades are the Japanese (Toyota, Honda etc). The rest are quite mediocre or worse, which doesn't exclude many happy owners among those brands. Besides, Seat is a VW clone, which puts it in a slightly better position.

I've used Peugeots and had a Citroen in the past. Good overall experience, very cost-effective. Either way, a single experience/opinion is statistically irrelevant, i.e. doesn't prove anything.

I'd buy some models of the three brands if they were attractive to me in terms of pricing and otherwise, but the same goes for ANY brand and model under the skies (and anything else, for that matter) .

It's a known fact that many people are willing to pay a bit more for comparable German makes & models which tend to age gracefully and achieve better resale values.

Getting rid of prejudices is a good way of finding good deals - it takes some time and experience, though.