I see this in Reston VA.

Real estate prices tend to be high. The mixed use development might have a few fancy restaurants, high-end boutiques, etc - but nothing to fill the daily needs of the residents. The local residents often have to drive to get to a normal grocer or mom & pop retail.

part of that, for LA at least, is that the mixed-use here still requires parking, which is expensive. so it's designed with low commercial square footage to make room for ground-level and above ground parking, which is cheaper than subterranean parking. the commercial space is minimized to a token amount likely to meet the necessary zoning/permitting restrictions to get the benefit of higher floor area ratios (FAR) for the least cost. then the businesses that can fit in the space, given the high rents, aren't nearly as attractive to residents, who are also paying high rents.

The apartment I rented in LA shared space with a Trader Joe, was across the street from Target and UCLA was a couple blocks away. Super expensive, however.

The Embarcadero Centre is mixed-use and pretty popular./