Go and look up the concept of money mules. Fraudsters don't need to setup bank accounts, they either buy bank accounts off people for £50, or convince people to move the money on their behalf by claiming they're doing an "accounting" job that involves large money movements, and the mule will get paid a percentage.
Most people don't realise what these accounts are used for, or just don't care because they're paid enough to look the other way. Then stolen funds are quickly moved across dozens of banks, with the money being split and re-combined with potentially legitimate money. Eventually the administrative overhead of tracking the money gets so great that no one bank can be bothered to do anything about, and the police aren't interested in actually investigating. The end result is that once the stolen money if a dozen or so bank accounts away from the victim, it's extremely unlikely that anyone is actually going to trace the money to that account, effectively making the money clean.