The general premise of the rental market is that if rents are high, the profits from building new rental units will justify the construction costs and then new units will be added until the rents go down, i.e. until it stops being profitable to add more.
This actually works unless you inhibit the construction of new units. Naturally that's what we've been doing, which is why it isn't working. But the solution is to stop inhibiting the construction of new units.
Because the alternatives don't actually work. Unless you can build enough units to meet demand, there aren't enough units. Which means you either have high prices which suppress demand because people who can't afford them are forced out, or shortages because you're imposing some inadvisable price controls and then instead of being unable to get a unit because you can't afford the rent, you can't get a unit because they're all occupied and no one is adding more.
Some states have solved this to some extent with the builder's remedy to override local zoning decisions.
And cities, like Seattle, still undercut this by taking way too long to review permits.
Seattle has more problems than that. They recently lost an illegal takings case where they used the scorpion and frog defense -- You should have known we'd apply additional affordable housing conditions that make your venture unprofitable.