In my opinion, the prevalence of square-based mapsheets over hex-based is locked in at the graph-paper level. It's a lot harder to draw a room on a hex map when the modules all have them drawn on graph paper.
Things start falling apart as the minis "wiggle" their way down narrow hallways, lurching left, then right, as they go from hex to hex in a 5' wide East-West hall.
It also has a lot to do with ease of access. I can get tons of 1" grid stuff, and I can fake it with desk-sized 4-quad and 5-quad graph tablets whenever I need to. Getting 1" hex battlemats generally means going out and buying one specifically for the game.
Personally, I actually prefer hex-based combat. But the logistics for the average younger gaming group can be daunting and it could turn a number of them away quickly when they first see it.