I don't get it much either, but I think one of the main selling points is the touchscreen. Sure, there are laptops with touchscreens (even ones that have the keyboard come off) but it's kind of awkward switching between keyboard and screen, and what's the point of buying a switcher if you aren't going to use the keyboard half the time? Seems like it's either full laptop or full tablet for most people, unless they go out and buy a Surface or something.
For the record, I've yet to see a Surface IRL, and this area's pretty densely populated
From what I've seen around my house, tablets are mostly used for their games. Laptops/computers are more of a 'serious business' sort of a thing (except for large, graphics-card-requiring games, but there's not many around this house), where one could do better with a typical, often quicker physical keyboard/mouse combo.
Also, tablets are lighter than laptops, so that's a point I guess?