For a long time, as young professionals aged into their late 20s / early 30s, they would move out of LA to suburbs in search of a big single family home with a yard, etc.
Demand for apartments in LA, particularly in the areas east / north of Hollywood, was therefore mostly constrained to professionals in their 20s and working people who did not have the income or assets to move out to the suburbs. (That’s not to say there weren’t / aren’t exceptions… we’re speaking in broad strokes here.)
It’s not clear what caused professionals to stop moving to the ‘burbs. The trend really began in earnest around the beginning of the Great Recession in 2007-8. So it may have been that professionals didn’t have the money to move or couldn’t get the loans.
Another explanation was that 2007 was when the first of the Millennials (the massive generation born roughly 1979-2000) hit the age when previous generations would have started to consider moving to the suburbs… but the Millennials basically said “nope” to the high consumption, high debt suburban lifestyle.
Whatever the reason, LA finds itself with a major problem / opportunity: The Millennials are staying in the city and competing with more traditional renters (the young and the working class) for housing, driving rents through the roof. So either the city is going to find some way to allow developers to massively increase supply, or we’re looking at rapid rent increases for the foreseeable future.