Here is a tool you can use to track rents. Rentslicer.com. They have a trend and graphs page that monitor rents in many cities including San Diego and LA. You are right avg rent is up in both LA and San Diego. This is sheer speculation but it seems that a growing number of people cannot or won’t purchase homes right now which is evident in the data which does increase demand for rentals. There are empty properties on the market that have not found their way to being rentals just yet. The population decrease while true is still minimal.
According to OCRenters bubbletracking 30% of properties are vacant right now. That makes this housing market insane IMO. Home prices are too high for anybody to purchase increasing the renter population meanwhile 30% of homes on the market are sitting vacant. Points to a MAJOR CORRECTION doesn’t it!
By the way the trends and graphs page on rentslicer only goes to April but the current avg rent is on the first page of the city report. So you can still calculate the difference.