IMO I think it’s because since tropical systems almost never hit SoCal (the last landfall was in 1938) and because of the dried up climate there (wonder why water in SoCal is so costly?) causing even 1 to 2 inches of rain to cause widespread flooding havoc (especially in mountainous areas, and the fact that there are no wetlands in LA to absorb floodwaters), people think the effects of even a tropical depression hitting the region will be equal to that of Harvey or Katrina.
Except…LA isn’t fucking Houston or New Orleans; Houston got pwned because they bulldozed nearly all their wetlands despite being on flat terrain (which LA isn’t), while New Orleans was a ticking time bomb (and still is) because of its low elevation.
LA is going to be messy on Sunday and Monday, but to suggest it will be a humanitarian catastrophe on the scale of Harvey and Katrina is just ignorance.