It's just not that easy. People running these things completely lack the understanding of just how seriously security needs to be taken. Various sites handle millions of dollars worth of bitcoin with "patch all flaws" style security. People need to understand that millions of dollars of easily disposed of goods are worth killing people for.

It won't be long now until we'll hear the first case where some employee of a third-rate exchange or something will wake up with a barrel of a gun pointed at him, forcing him to go to work and turn over all the float at his company or have his family killed. It's been done in the USA, and for much less than what these exchanges and mining pools routinely manage.

Banks have security against this sort of thing. They manage it by making actually keeping that money after obtaining it without getting caught really hard. I have no idea how it can be protected against when it's bitcoin.