What's a proxy purchase?

Edit: never mind, Google told me. It's getting the older kids to buy you alcohol.

or get homeless guy/junkie to buy 10 sim cards/prepaid phones for 20$

And you know - stolen credit cards might even give them an actual conviction they can make stick "Al Capone style", instead of trying to convince a jury that shittalking in a Zoom chat was a real threat...

Right, but there is always something to go on there, who made the purchases, where was the card stolen etc.

At which point you find a trail leading to some Russian hackers who stole the credit card and then sold it for cryptocurrency over the internet to the person you're looking for, who they have never met.

It's square one. It's no easier to trace the anonymous buyer of a stolen credit card than the anonymous Zoom user to begin with.