The answer is very simple:
Because you can not make fiat withdrawals, no matter what you do (try to verify your account, write to support, etc).

Is just an scam.

They are expecting that you put your BTCs into, sell into fiat and then... YOU ARE TRAPPED!!!

The exagerated price is because the people are triying to re-buy BTCs so can exit fron hitbtc, because they can withdraw BTCs, but they can not withdrawal fiat...

Is a first order Scam.

The same thing is happening right now in Cryptsy... you can put crypto in it, but the withdrawal system (via Tether) is not working, so... the prices arises.