Why are all the dating sites including match.com and even Tinder full of scam artists using fake pics?

Because scammers know that people who go on dating sites are lonely and sometimes desperate, and those are the ones who are the easiest to con into sending money. There are also people who are married who use fake pics so their spouse doesn't find them. And there are people who are just cruel and get off catfishing people and playing with their emotions

Because, people can be d**** and are desperate to hook up with someone as they have self-esteem issues or just want to troll around.