They never left. But unlike when they started as a new thing, now the scammers are getting de-platformed. And more people can tell the difference between a scam and a real project, so the scammers don't really bother anymore.
So instead of 1000 scam ICO projects we have a few real ones. Although I admit the scammers did inflate the hype back then.
I agree, and most of the ICOs are just scams and just to gain money from investors then they will do an exit scam. And I think that they switch to an airdrop scheme and " pay more to gain more airdrop" and to bait people into gaining more tokens but apparently they are just getting scammed and developers are gaining money.