This is only true when looking at tech companies that really hand significant stock grants. There are tons of software developers, all over the US, getting only salary and modest bonuses outside of those few places that grant stock that is as good as money.
When you look at that world, contractors still win by a very wide margin: They are organizations where HR will not allow a hire for a competitive salary, but a department head can spend their budget on contractors any way they want. This leads to gigantic pro-contractor differences: As recently as last year, I made three times as much as someone sitting next to me that had Architect in their title, and the contract was for many hundreds of hours, so it's not as if there was non-billable overhead.
Now, the big tech companies can compete with contractor billing rates, just as long as it's either Netflix, or someone with good-as-money stock grants, but if you live in, say, Kansas City, you won't smell those companies anyway, and chances are that, barring remote work for a giant, the best you can hope for without contracting is salary that isa little bit below Google's, but no stock.