Who is “they”? What jurisdiction?

The country in which businesses are being targeted. Crypto is a payment implement for crime. If the US outlaws buying crypto, companies in the US can't pay their ransomware bills and so will no longer be targeted.

I don't think you can put this genie back in the bottle. The US is a corporation cooperative and the banks are already in crypto and only raising their holdings.

Even if the US bans it, it just moves the market more into the dark. Ransomware will still happen and still require crypto payment. The only difference is the hoops companies will do to acquire this crypto in a semi-legal way (probably by using multinational entities to route payments).

That would be a gift to every other country that doesn't follow suit.

That would be devastating to any country that doesn't follow suit. They would be the ones targeted by ransomware. So not only would they get all the ransomware attacks, they would also get all the negative value crypto creates. Since it doesn't create any positive value, that would be an excellent big brain move.