Money mules

Good evening,
Recently I met a person who got involved in money muling in the past by letting some gang use his bank account to transfer funds. Now he cannot open any account anywhere.
For how how can he be banned from the banks? How come that he avoided jail if his name and address was known to anyone interested in tackling fraud.
And by the way, what is the point for crkminals to have money mules and transfer funds from one account to another, then withdraw cash and so on? I assume they already have large sums in their accounts, so why to spread all that across mule accounts? And how do they deposit illegal money first before being able to spread them?
Logically they could just keep it in their account instead of paying mules and wasting time for withdrawals?
Any thoughts?