Well, MSBs are held criminally liable for any illegal activity their platforms help facilitate. Banks can be fined heavily (see: HSBC, Wells Fargo) for such behavior. It's ironic their customers can be held criminally liable but they cannot... that's another conversation though.

But yea it's all a game of risk and how much of it they are willing to take. Bitcoin businesses are in the highest of high risk categories and they currently don't bring in enough money for the banks to justify the potential downsides.

At this point any US based entrepreneurs should consider looking elsewhere for banks. I know of a Caribbean country planning to be a haven for cryptocurrency businesses. Things will be announced soon.