One demographic I would expect traditional mouse usage from would be gamers. When I play a first person game I always use my trusty old intellimouse. Otherwise, I use the trackpad unless I'm simultaneously using my mechanical keyboard, but if my keyboard had an attached trackpad I'd probably be using that. But mousing in general just isn't a very important to my workflows and trackpads work just as well as mice for nearly all tasks. Arguably they work better for some since you don't have to move your hand far from the laptop's keyboard to use the trackpad, while using a dedicated mouse means taking your hand completely off the keyboard.
