But who's selling the land? If everybody has to pay the tax then all of the property owners can increase rental prices by the same amount.
In fact, I'd argue the majority of landlords are shit investors sat on fairly low yields
You're right that some people will get squeezed out, but in high demand markets there are enough people willing to pay that it doesn't matter. The number of properties available for rent in California isn't growing as fast as the total population is growing. Property owners will eat the 5% increase for a while - at least until the existing leases expire - but eventually they'll incorporate that 5% increase into the rent.