In the U.S. you don't have to give a reason for taking out your cash (though withdrawals over a certain amount are reported to the Feds). But there are ATM limits. I always assumed - perhaps naively - that the reason was to keep the ATM from running out of cash too quickly, thus minimizing the cost of replenishing them. And occasionally, on 3-day weekends, I have seen more out-of-order ATMS than usual. . .presumably because they had run out of money.
My impression is that it's to limit fraud. If someone steals your card an your PIN, the daily limit keeps the amount they can steal from your account before you discover the fraud reasonably low.
If for some reason you need a bunch of cash from an ATM, you can generally call your bank and have them temporarily raise the limit.
"The elimination of withdrawal limits enables the participants to withdraw literally unlimited amounts of cash until the operation is shut down," the U.S. attorney's office said.
