No basements in western states :)
If the frost line is lower, then a basement is very little extra cost since you are digging deeper and laying more concrete anyway.
If you are building on a hill, then making a 3 story house is also very little extra cost.
Anecdotally, finished basements are practically required if there is any sort of hill, which fairly common in the west, whereas they're likely to be absent for houses built on the floodplain.