I got this feeling most folks buy MTB because of the versatile of the bike, then used as a commuter. When I was considering commuting by bike, there were many factors that lead me to start with a MTB. I bought a Walmart Schwinn MTB in plans to do my commute. No it was not for looks or anything like that. For one, it was something I can afford to buy and get stolen. I rode that thing everywhere around town to get used to not having to drive. When the darn thing started to skip gears and the rear wheel got knocked out of true, I went to shop for another commuter bike even before I was commuting.
The second bike I decided on for commuting was a Specialized Hardrock disc. Again it was not for the looks or anything like that, but rather because I needed something for commuting weekday and dirt trail weekend. The versatile of a MTB was what made me buy it. Luck has it's way and financially I was able to afford a roadbike and turned that into a commuter and started my commuting.
If my finance did not turn as it did, it would have been MTB for commute since I can take that on or off the road but I cannot take the road bike to the dirt trail.