Saying they turn into a scam is wrong because they start as a scam since day #1 , most of them don't even have mining equipment even If they tell you otherwise. If you really want to invest then stick to trading or even better ... HODL your coins for long term.
You are correct,most of those cloud mining site did not last long. I even joined a couple of sites as of now, only hashocean is left. Also I agree with thread starter that after halving,many sites deactivated.