[lazide]

Ground moves, especially in California. Sometimes it’s subsidence, sometimes landslides, sometimes it’s seismic related, sometimes it’s frost heave or the like. Properly studied and buried (with proper backfill) usually is protected, but big enough changes will cause problems.

Throw in backhoes, erosion, etc. along with it being more expensive to fix when it does break, and overall it isn’t always guaranteed buried will be cheaper maintenance wise.