Wrong. Seattle, Oakland and Los Angeles are mostly built on much flatter parts of those areas. California entire geography is about "Hey, check out these massive valleys or coastal land we can build in." Same thing with Washington State, Seattle is in between Cascades and Olympics where there is all this flat land to build on. Yes, they running out of land and building into mountains now. That problem is like having FAANG scaling problems. It sucks but it's good/manageable problem to have and you have massive checkbooks to help solve it.
Have you been to Appalachia? It's not on the coast and does not have these benefits. If you want to compare it to West Coast areas, it's more like Sierra Nevada. Inland Mountains with only small valleys to build infrastructure in.