What if they weren't actually hacked?
The site owners could simply be stealing the money and faked a hack attack to allow them to get away with it. Spreading the loss around is just subterfuge to keep the ones who were "hacked" happy by giving them something. It also justifies evidence showing that Bitfinex is going into every individual account to add/remove something - to add noise to those trying to track down the source of the "hack". By the time people figured out it wasn't a hack, the site will be shut down and the owners (who have likely planned this from the beginning and operated under fake names) long gone with the loot.
There's nothing preventing the same thing being done at other bitcoin "banks", which rather belies calling them that.