SD @ 20K not 10K
The graph shows SD inventory at 20,397, not 10K.
The labels are above the very faint axes making it difficult to read. However, when you select a particular metro area the actual number shows up at the top of the page in the figure title.
OC inventory : 15,990
LA inventory : 80,129
LA is 4x SD inventory. The population ratio for the LA vs SD is probably > 4x (not sure precisely how it’s defined), so anticipate that the per capita inventory is closing in on SD.