The biggest bitcoin sites that close and the scam i know is the popular cloud mining company, Hashocean which i also invested in with at least 0.5 bitcoins way back then because i was so attracted to the posts of investors in different social medias because they are earning a lot of money so i also tried it but didn't work and they closed and ran away the bitcoins and now for sure they are relaxing to their dirty money but it was a lesson for me to not trust anymore on either hyips or cloud mining.
yeah, It is hard to not agree with your point of view, because Hashocean was indeed a really huge ponzi/scam site, it was online for a really long time ( somewhere between two and three years ) and it was actually looking kind of legit- they have been sending their mining machines to the users that demanded it ( they has given such an option, after reaching some specified goal, such as xxx GH/s.
But I have never deposited any money in there, I was really aware even in times when I was a little bit like "I should have invested it " because I heard about this project freshly after it was created.
The returns they promised was really too attractive for me, something was not right in the whole operation, so I decided to stay away- and i did a very good thing.