It's unclear how you believe the label attached to something to be useful.
Suppose there is an "artist" and you like their "art" and want to commission a piece. You send them money for "art", they email you some doodle or AI-generated image and simultaneously mail you some drugs.
Assigning the label "art" or "code" to the payment doesn't provide any information more than having no label whatsoever, because the label is a lie but the only way to prove the lie is to uncover what the transaction is actually for, which the existence of the fabricated label doesn't help you to do any more than having no label at all.
Establishing what a payment is actually for is not something the payments system is suited to do and attempting to use it for that causes only problems, because the honest users who put down something legitimate that makes the bank skittish are unjustly harmed, whereas the actual illicit users simply lie because there are several easy lies with no viable way to verify the contrary.
Yes, I agree that this may be beyond the scope of a mere "payments system".
"BuyMeACoffee" appears to be a Patreon-like platform for "artists and creators". I would say it is more than a payment platform, because it is a marketplace and a venue for people to do business.
Now we have plenty of marketplaces, such as eBay, or Etsy or Amazon. These marketplaces have strict requirements on what vendors and customers can do and how they can transact business. If you went on Amazon and purchased art+drugs, that would quickly be shut down. It's also Amazon's responsibility. Now they are brokering those payments from customer to vendor but they are more than a payment platform, because they are hosting both parties.
BMAC is not merely, blindly transacting payments like Visa or Mastercard. They're providing a venue for stuff to be put out there. If they are collecting payments from fans and disbursing it to creators and artists, then I say that they have a responsibility to ensure no illicit activity goes on and people are getting what they paid for.
"Getting what you paid for" is obviously an extremely subjective thing when we're talking about electronic art or media, and especially when customers can buy "memberships" or send "tips" because now we're just funnelling money to a personality influencer who is into crowd-pleasing. And the opportunities are vast for organized crime and nation-state threat actor sort of activities when you scale that up and go crossing international borders with your service, wouldn't you agree?
In meatspace, you're going to have a comedy club or a concert venue, an art gallery, you know, someplace that showcases artists and may sell their work, or enable them to work for money. And any such venue will necessarily have controls that protect the customers, and protect the artists, and if there is money changing hands for illicit purposes, the venue is on the hook for this. Because they're doing the matchmaking.
And there are mainstream marketplaces that are doing this, but to do it large-scale and internationally is going to run up against legal and regulatory hurdles and it's not as simple as turning a blind eye.