Why would a credit card company do that?

For profit and compliance with authoritarian government.

I really don't know. But they must have reasons I don't know about.

We can only speculate as to their internal motivations. But why doesn't really matter when we can watch them actively do it.

Because they can, and people with influence know they can. Then people with influence force the credit card companies to do it. Not hypothetical, in actuality

Are you actually concerned with their motivations, or just unaware that this is a common practice already?

I'm a big fan of card payments myself, but I agree that cash should be accepted universally, until unbanking/underbanking is completely solved and there is a cash-analogous private way to pay.

Besides the accessibility issue, not nearly all activities or situations making somebody want to transact anonymously are illegal (just consider e.g. people in unsafe domestic situations trying to get help/away but not having their own card).

I believe we could strike a pretty good balance with some research, engineering, and product development, avoiding both possibilities for tax evasion and financial crimes on one extreme, and creating a complete financial panopticon on the other.