It's a "stop shooting yourself in the foot" win-win.
Like, the last time I did a back-of-the-envelope, physical spam mail was also a surprisingly large (but still tiny) fraction of US CO2 emissions. We could just stop sending spam mail, and save like a quarter percent of the US CO2. Not big, but you're also not losing anything of value.
> Ending crypto mining is the easiest no-brainer in the history of energy systems.
Ending any profit-generating activity is incredibly difficult. I suspect you're not referring to ending it, but allowing it to be transferred offshore and losing the ability to regulate it. But if it's banned in the US, good luck getting every other country on earth to ban it in solidarity.
Considering how broadly unpopular the idea is to average people who don't aspire to own cryptocurrency (especially after FTX publicly ate its own organs) I don't see it being particularly difficult to find support for such laws in more liberal places such as the EU.
If you reduce it by 50% you save 50% waste. If you reduce it by 75% you save 75% waste. You dont' have to entirely wipe it out to save a lot of waste, just make it harder and/or more costly.
Attack the supply side, attack the demand side: tax it, regulate it, cap it, replace it. All of these can reduce the mining so they are all useful.
edit: to answer your idea that they will just move...
If these other places were as good or better for mining than where they are now, they'd already have moved. If you make them move to a worse mining situation, that's just proof that what you're doing is working.
Like, the last time I did a back-of-the-envelope, physical spam mail was also a surprisingly large (but still tiny) fraction of US CO2 emissions. We could just stop sending spam mail, and save like a quarter percent of the US CO2. Not big, but you're also not losing anything of value.