Rental prices stay surprisingly steady even when house prices go insane - compare similar apartments/houses in major expensive cities and cheaper ones.

Sure but the rent will follow the increased purchase price. They also don’t go down, or at least they’re extremely sticky.

They're limited by what people will pay - and "techbro" cities have people with insane salaries willing to fork over big bucks. But there are similarly expensive areas that don't support the income necessary, and there often you find huge rental inversions.