I think this is correct. A lot of these buildings seem to be post frame or poll barn style. Relatively cheap for building large square footage buildings but add some limitations to multiple floors. Even if you put the storage floor under the shopping floor you'll run into tons of issues with buildings of these sizes that don't have a ton of pillars for additional support. I mostly see these stores built on vacant "rural" land on the outskirts of cities rather than in city centers themselves. Which means the single floor square footage is rarely an issue and not something worth designing a building around. If you have all the space you need to go wide, it's almost never worth going tall.