Hopefully this equalizes out over time as more tech companies can properly adopt remote workers and thus even out the employment field away from centralizing in a few specific cities but we are a long way from that.
I used to think that way, but in, like, the late 90's/early 00's. "Surely as internet access and software tools continually improve, remote work will become better and more common, democratizing blah blah blah."
Instead, while the internet getting better definitely happened, the pay differential and clustering effect in major tech hubs only increased.
As for why that would happen, I have a few different thoughts, but I think the gist of it is that the internet getting better spawned huge internet giants like Google and Facebook, and organizationally it's still an advantage to have people colocated so they went with that.
Or, that’s where companies are and they’ll take what they can get in the area because they like having warm bodies in the office rather than dealing with better qualified remote workers (like practically every company)?
On the other hand, non-collocated teams are challenging and if you have very little experience running a team (as many young founders do) it might be wise to hire locally -- at least at the beginning. I think a lot of founders also probably underestimate the amount of time they'll need to get off the ground. So if they have $5M, it might seem OK to have a burn rate of $2M per year (I'm using pseudo-random numbers). They'll think, "If we can't get another big round in 2 1/2 years, then we might as well move on to something else". So they are willing to pay the money.
Not anymore, someone will be following the "locality doesn't matter mantra" and will outbid you. What you are saying might be more true for entry level or very generic skill sets. But if you are hiring top talent, you have to offer the same best offer everywhere, because if you won't then someone else will.