LA is fortunate in that it doesn't suffer from freeze/thaw cycles and can put down a lot more concrete without worrying about expansion/contraction and water ingress.

I've noticed that a fair amount of concrete sidewalk in Los Angeles appears to have been poured when the neighborhoods were first developed (as in post-WW2) and haven't been removed or updated since then (at least based on the date/contractor stamps). Again, the lack of freezing weather, wide streets that don't necessitate parking/loading on the sidewalk, and fewer tree roots to uproot/disturb the gutters and sidewalks means that the original infrastructure is still in use.

More to the point - creating curb cuts is more than just customizing concrete forms. Oftentimes you'll need to regrade the surrounding area to reduce slope, move any in-ground utilities, and revisit any other updates to building codes (such as the bike lane stuff mentioned in the article). Not everything in/under the streets is owned by the same city/county/state/federal department/private org so that further complicates the work.

If only the real estate speculators that settled this swampy valley had considered this stuff in the early 20th century...

Worth noting that LA does not have freeze cycles. I wonder what the pothole formation likelihood is as a result.

Interesting! Is it possible to make the ramps offsite and then fit into place?

EDIT: I'm assuming the difficulty here is the pedestrian ramps at intersections. NOT the curb that spans the entirety of a road section.