This is one of the biggest hacking and exploit forums, so naturally scammers will thrive here, that's just how the community is.
Reputation means nothing because someone with good rep could just do a big exit scam the next day and you will never know, but that's the only measure for how trustable someone is whether you like it or not. So why should a seller with an already established reputation risk getting chargebacked by some random like you on Paypal when he could guarantee his money would be safe with crypto?