"to protect customer funds"

Most people read this wrong.
They believe this says that the customers have funds.

But in reality, when you "put money in the bank" you are giving your money to the bank (to do with as they please)

So, there is an account called "customer funds" and the bank doesn't want to see that account raided by people. They want it protected from leaving the bank, and even more so, leaving their system.