Housing costs do tend towards ability to pay, and when there's scarcity, that "ability to pay" starts cutting out those with the lowest incomes, since they do not get the housing.
That's how housing costs can increase faster than the income of an area, it's the market displacing those with lower incomes, and readjusting to only house the wealthiest.
Add in that housing prices are distinct from the housing costs, and that leases only change rent occasionally, and lots of people are owners and have fixed costs, and prices can rise quite a bit faster than incomes.
Population may have flattened, but a toooooon of people were looking to move suddenly to new areas, which is another way that scarcity is created.
Your chart is the number of units under construction, but that high number doesn't translate into more new homes than ever before, because completions have been massively delayed. So there's a lot of homes sitting half finished as they wait for supply chain crunch's to resolve. And to compare this to numbers from the 80s means normalizing for length of construction, something which is getting delayed more and more.
Overall, construction has massively constructed since 2008, and even before that it had been trending down for a long time.
That's how housing costs can increase faster than the income of an area, it's the market displacing those with lower incomes, and readjusting to only house the wealthiest.
Add in that housing prices are distinct from the housing costs, and that leases only change rent occasionally, and lots of people are owners and have fixed costs, and prices can rise quite a bit faster than incomes.