I posted about this as well.

One thing that I have observed is STEEM and BTS wallets are generally in maintenance mode for longer on many exchanges when compared to other coins. I am not sure what the reason is. Is it because there are less BTS and Steem in circulation when compared to other coins or is it because of some technical challenges with these coins.

Sometime I feel that it has something to do with the zero transfer charges. May be exchanges cannot make profits when people withdraw from their exchanges as the transfer charges are zero. If not it should be the easiest as Steem 3 second transfer rate and hasslefree when compared to other coins. What do you think? @kingscrown