As always,
Wikipedia to the rescue:
Basements in small buildings such as single-family detached houses are rare in very wet climates such as Great Britain and Ireland where flooding is a problem, though they may be used on larger structures. However basements are considered standard on all but the smallest new buildings in many places with temperate continental climates such as the American Midwest and the Canadian Prairies where a concrete foundation below the frost line is needed in any case, to prevent a building from shifting during the freeze-thaw cycle. Basements are much easier to construct in areas with relatively soft soils, and may be foregone in places where the soil is too compact for easy excavation. ...
I would guess that the Southeast at times falls into the "wet climate" area and definitely into the compact soil category. But I expect the real reason, which is something that I had never considered, is simply that, according to the article, you
need a buried concrete foundation in the midwest, so you might as well put in a basement. Down here you don't need one, so it's an added expense, plus increased flooding potential. Recent tornado issues do make a case for a basement, but I've been down here over 10 years now, and that's the first time I've seen anything like that. Living in Ohio, I seem to remember tornadoes being a much more common occurrence, although seldom with the damage we've seen here recently. More common down here are hurricanes, which come with a lot of water, so, again, flooding becomes more of an issue. Even with the wave of tornadoes we saw a few weeks ago there was flooding. So while you might think with all the attention the southeast has gotten lately that tornado shelter would be an issue, it really isn't an issue most of the time, and when it is an issue, a basement that's rapidly filling up with water might not be the safest place to take shelter.