I put a hitch on my Subaru Legacy GT. Installed it myself. Easier to load bikes and no risk of the $20k accident where you trash your bike/car/house all at the same time.
The big reason is cost. Many SUV come with a hitch as a factory/dealer install prior to purchase so its already in the sticker price. For a sedan its an extra $150-200. That's a lot more expensive than the standard trunk mount.