The short answer is, compliance.

There are "know your customer" laws. Some banks have taken hefty fines for turning a blind eye to money laundering. It's not that they necessarily knew that their customers were laundering money; it's that the activity was suspicious enough that they should have known.

So, anything that looks like it might be money laundering (or otherwise shady) gets shut down. They may be making money by having you as a customer, but it's not enough to risk the wrath of their regulators or the justice department. So the baby gets thrown out with the bathwater, so to speak.

I'm not an attorney; maybe someone who is can give a better explanation and/or correct any mistakes in what I wrote.