Do you know why exchanges seem to be having difficulty offering a stable service for steem?

Currently there are crazy times because of Bitcoin. Aside from that:
Bittrex is indeed having some delays recently but they are great at communication and I think we would be able to help them improve reliability.
Blocktrades is working flawlessly.
Poloniex well... multiple attempts to contact them, they were down today for hours... that's not related to Steem at all.