Bing a contractor, there are several reasons for no basements in the south and Texas (Texas is it's own entity. ask anyone from Texas!). Water table and soil composition are the main ones. Lots of wet clay soil in the south so moisture issues and clay soils expand and contract which can cause major issues. Water table issues anywhere near the coast/rivers and bedrock issues when you get inland to the mountains. Easier to build up.
Only seen one hot water heater in an attic. Worst place to put one! Lots of air handlers in the attics in the south which is also the worst place to put them! Unless the attic is sealed and part of the building envelope. 50',60's, and 70's the tech didn't exist, so only place to put them unless you use mini splits