Because if you have a stolen identity and open a bank account, as long as that account isn't trying to defraud the bank (e.g. write bad checks, commit ACH fraud), it can go on living for a long time before it's discovered and closed.
In this case, they opened up a bank account with stolen identity, and then used that to get their Spotify payouts, and then eventually transferred that to another account (cash, crypto, whatever). From that bank's perspective, unless they were specifically informed of the bad account, there wouldn't be a ton of unusual activity that would flag the account.
Why would a stolen identity not being used to steal from the person whose identity was stolen, but just to process legal payments, be noticed in a few days? Or even a few years? Maybe at some point the IRS might find the account that used my identity and send me an angry letter, but that seems like it would be years down the line.
Also, how do they succeed in keeping this scheme for more than a few days after the identity theft is noticed and reported to the police?
And why would they not just take the very music they just bought and paid for, and publish that as any other artist do? There's no crime in buying the rights from another artist -- that's exactly what all music labels do.