Because there are no jobs there.
Yes remote might fix that, eventually. But I strongly doubt that, especially as humans are social animals.[1]
However The UK is a more extreme version of this. People move to london because it has the most concentration of high paying jobs, and as a side effect culture (what that is I leave up to you. I don't just mean music, cinema and posh people shit.)
Now, I could move back to bumblefuck rural england, but I would have to exchange an underserved IT job market, with a median wage of >£60k to a once/two company town with a median wage of £38k. Combine that with houses only being 30% cheaper, and higher transport costs, no nurseries or comprehensive child care, the countryside can be a real pain in the tits.
Costs are higher in the countryside, as there are less public amenities.
So no, people can't just move, otherwise they would have done already.
[1] there are two classes of remote "influencers" the first ones seem to be happy working alone, permanently. The second appears to be the ones that are "jet setting" where they work in a new country every other month. Both of these groups represent a tiny minority. I strongly doubt that we should be optimising for these two noisy classes of people. I suspect, and me, my team and wider company data backs this us (even though its shallow evidence) that they more popular route is hybrid.