Philips puts together a pretty good 3 legged stool analogy: supply, stability, subsidy.

Supply: Unless there are enough homes for everyone, people will get priced out. The region has added jobs faster than housing for decades, and we have a serious supply problem. Adding to the total quantity of homes is necessary but not sufficient.

Stability: tenants need protection. Even when there's enough supply, people can still get screwed by landlords, and we need to have good protections.

Subsidy: even when there's lots of homes and tenant protections, not everyone can pay market rent. So we need subsidies.

Now, the subsidies go further when there's more supply. The tenant protections are bolstered by the ability of tenants to go "f this I'm moving" and find another apartment.

All three reinforce each other.