That would be a change from preventing illegal transactions.

As it stands currently, the risk associated to the company for allowing illegal transactions is what drives their policy since they get brought into lawsuits for allowing monetization of illegal content in some jurisdiction.

Changing it (world wide) so that payment processors are not subject to money laundering laws and cannot be held liable when a merchant sells something illegal would allow them to change their model to allow all lawful transactions and not have false negatives.

Until false positives (allowing an illegal transaction) is not a risk for them, their policies are unlikely to change.