In Arizona, everything was slab-on-grade because the ground was very, very dry. That's not so in most other areas.
The crawl space keeps the wood off the ground where it wicks up moisture and quickly rots. Cement wicks up moisture, too. Try a slab in Seattle, for instance, and your house will soon be uninhabitable from mildew.
> 30 percent of new single-family homes started in 2013 have a full or partial basement, 54 percent are built on slabs, and 15 percent have a crawl space.
Since 2000 most homes have been slab construction 60/40 by 2013 78/32.
It is cheaper and quicker to build slab and the way the housing market works means that developers choose what to build.