Because Bitcoins are virtual. You can hide them on a server somewhere in an encrypted file that nobody can crack if you really want to. I'm not saying it's impossible to have them stolen, but compared to hiding a lump of gold or an art piece or simply tons of cash, bitcoins are easier to secure.
Nobody robs banks anymore, smarter to try houses.
Safety deposit box. Nobody robs banks anymore, smarter to try houses. Less risk, fewer panic buttons, better chance of good cash on hand.
10/10 most secure computer ever