I never quite understood the bugabear about money laundering in the abstract.
If there's fundamentally a criminal or security problem, it seems like that should be the core thing that law enforcement should be chasing.
Disguising the source of funds, while arguably distasteful, shouldn't be the issue as long as appropriate taxes are paid. It's amusing that the IRS has explicit "declare your illegal income and we are not allowed to turn you over for doing so" mandates.
My guess is that it provides a simpler case for prosecution. So to speak, they'd rather go after Al Capone for tax evasion. Rather than having to build a case on the "base" crime-- "prove he sold specific drugs at a specific time" or "prove he was involved in a specific deal with $sanctioned_country" -- they can move to "prove that this neighbourhood Subway franchise isn't turning over $75 million a year", which can largely be proven with a couple people sitting over Excel, rather than on-the-ground investigations and witnesses.