Short answer
Plans often get rejected because site constraints, code notes, dimensions, energy documents, structural coordination, or city-specific requirements are missing or inconsistent.
The drawing set contradicts itself
One sheet says one thing, another sheet says another. Plan reviewers notice. So do builders, usually at the worst possible time.
City-specific rules were treated as generic
Bay Area cities vary on submittal rules, ADU interpretation, planning triggers, wildfire overlays, and utility requirements.
Engineering is late
If structural reality arrives after design decisions are locked, expect revisions. Build the team sequence correctly.