Even then, there are a lot of stations that upgrade the signal to make the station more attractive to buyers. Classic example is KGBS, when it went from daytime to fulltime as KTNQ. Rumors all along were that Storer was looking to unload it for a full-market price, which it couldn't get as a daytimer. People figured when TenQ made a splash (to the extent that it did) that Storer would keep it, but they put it up for sale within 18 months of the upgrade.
The issue in LA is land. Not just the cost, the huge NIMBY factor of putting towers in the air. Where I lived in Glendale, we had almost zero cellular signal from all four carriers, but efforts to locate cells anywhere nearby resulted in protests, RF claims, and, 12 years later there are still no towers.
Finding a site that would accommodate multiple towers in the right location would be expensive... likely more than the station is worth... and would barely improve coverage at all due to protections. KFWB abandoned their 50 kw CP for somewhat similar reasons of high cost and no real signal gain except in the main lobe that headed towards Catalina and points west.
Another issue is that the permitting process could take years. One station in Miami that moved to the far west side of town took nearly 10 years to get all the needed EPA, hazardous waste, city, county, FAA and other permits.