The answer is - while YOU may not care if banks are forced to accept money from illicit (meaning immoral) sources, conservative businesses DO WANT a say-so in these matters.
Just because it's legal doesn't make it right.
May I presume you still oppose abortion? It's legal, right, so who are we to gripe about our TAX DOLLARS paying for infanticide, right?
The example you posted shows banks are not so forced: "My bank (top 50 in the US) does not accept accounts from sex industry businesses or from predatory payday lenders."