Yobit wallets that go into maintenance are due to:
1) dead chain (no miners)
2) broken chain
3) lack of interest as it then is not profitable to run a daemon
Wallets go into maintenance when there is a delay in the blockchain. If the chain starts to move again within a short space of a few hours, the chain will automatically go out of maintenance. If the delay is extended, the maintenance will become permanent and will only be brought out of maintenance based on a support ticket.
There are one or more bots on Yobit that pumps coins that are in maintenance. The trader chooses these coins as it is then not possible to quickly deposit coins to sell into the pump. Only those with coins already on the exchange with these coins can take advantage of the pump.
There are lots of things a community member/dev can do to prevent a coin going into maintenance. It is almost a dedicated job to do chain management and analytics for a coin, but it is important as a healthy chain will prevent a coin going into maintenance. It is always better to prevent than to cure.
None of the above is sinister though and looks to be part of a normal business model.
Or Yobit is functioning as a fractional reserve and selling those altcoins for BTC & LTC ,
Then placing those coins in maintenance where they never have to worry about pay out.
FYI:
The Majority of those coins in maintenance have active communities and working coin networks.
If Yobit is not going to have a working wallet, but just list everything in maintence for years , they be doing everyone a favor by going thru and delisting any coin , they are not going to support. Until they do, they are just a scam site.