Because said cities cannot get enough tax money from property tax (blame Prop 13) so they need to get it from businesses. But then those businesses attract people in the area and then those people need a place to live in but they can't get a place because nobody has the incentive to sell when your tax rate is locked in (well, growing up to 2% per year), on the contrary, you don't want to sell and then buy somewhere else and have to pay more taxes than you were paying at the old place, even if the new place is much smaller.

One of the countless negative consequences of Prop 13.