I think NYC almost certainly has much large prevalence than LA given hospitalization data alone.

One factor could be the nature of transmission. Regions where transmission occurs with high viral loads entering at the point of infection (for example, hospital-acquired infections) could see more severe disease progression. You would therefore expect a high hospitalization rate relative to prevalence. It's possible in other regions, including CA, hospitalization rate as a function of prevalence is lower because acquisition is largely at lower viral loads resulting in less rapid and severe disease progression. This is, of course, a hypothesis and very likely not correct. Time will tell.

Other important factors include age distribution of infection, as well as weather conditions and prevalence of pre-existing conditions.