The main challenge there as I understand it is that the Steem ecosystem as a whole is intended to be decentralized. Being able to directly withdraw from steemit would require a central authority doing the trades from Steem -> Other Crypto -> Fiat.
Someone could start up a fiat exchange directly with steem - but that would require fairly significant risk, overhead and couldn't expand globally all that easily.
I see, is there anyway around this?
Although, if Steem ever makes it onto CoinBase I will be happy. I actually trust them, but do you think it will ever be traded on there?