Along with the large amounts of growth, wages in the upper middle class have really increased a lot. If you look at tech workers, it was pretty common to see average tech employees pulling in $75k-$150k a decade ago; today employees at a similar level and set of skills are pulling $200-350k. As a result, there's a ton of money in the high end available to purchase housing in the area.
Saving for a down payment is a challenge, but less so if it's relatively easy to tuck away an extra $100k a year. This is likely available to a tech earner but not the Seattle hair dresser, unless they have also increased their asking rates for a haircut the last few years.
In a truly fair market, the new tech class buys newer, larger homes or apartments while the hair dresser buys their old starter home or bachelor pad.
If you're talking about cities like Seattle, the reason that a 30-year-old hairdresser would have a difficult time purchasing a place is because prices have been pushed absurdly high due to two factors:
a) a housing shortage (primarily in the SF Bay Area, but Seattle has similar problems, and the SF housing problems spill over into other nearby cities)
b) speculative purchasing by foreign entities
The second point is less relevant Seattle than it is to nearby Vancouver - and nowhere is it more true than in New York City - but it still has a huge inflationary impact on property values in a way that doesn't benefit any local residents at all (the properties are used as places to park money by people who don't live there, and may never even have visited the US).