Im sure nobody buy accounts, only who want to promote scam and other stuff. Or why would a normal people buy a legendary account for "xy" bitcoin ?
Because of the legendary rank and green trust of account. It is very hard to rank up account nowadays because of the merit system and also the green trust is very important because it means that the account has a previous successful deals which is very dangerous once it is sold to the wrong hand.
You can easily trust a legendary rank compared to a copper member and a 200$ is just a small amount for a scammer. It's either a scammer or someone who will used it to join on signature campaign to earn more money. I don't believe that the account has good post quality because if its indeed have a quality post, the owner will not gonna sell it because he can earn that 200$ within a month.
yeah, it is probably useful for scam only, but one can also use it for signature campaigns and earn money, it is not easy to get enough merit for legendary or hero rank
on the other hand, there is a lot of hero/legendary accounts obtained prior to merit system, which would not reached that level, if merit system was there from the start