I give them props for their AML and anti-fraud systems, which are why those limits exist. I was maxing my buys through them for awhile, and started getting hit with those high-risk letters. Complained to customer service, talked to them a bit, and they whitelisted me so I don't get hit by that. Really liked that level of customer service. I know my mainstream bank doesn't give it to me, no matter how much cash I run through/store in their system.
The anti fraud system called "high risk transaction" is an intricate system to defraud the customer. The reason is because you don't gain any extra info by receiving the ACH transfer that would dictate the chances it would be fraudulent. Verification of bank is all the info they have and they could very well reject prior to taking the money.