These bad actors perpetrate exit scams, right pulls, identity phishing(I have been a victim of this in a bounty campaign, unfortunately) etc.
Whenever there's new in the space bad actors and actresses will always be there to do something bad that's no news in the crypto sphere or even on traditional market. Though traditional now is something getting low more of this are now online as it wasn't that yet regulated yet especially crypto.
If I were you try to be picky sometimes picking projects, bounty or always DYOR if you're trying into investing. DeFi will one day be surpassed but few ones will stay.