Personally... convienience, comfort, and fun... in that order. I rarely ever have to worry about finding a restroom when I'm away from home. It's just nice to not have to deal with the hassle of it... go wait in line for 10 minutes just so you can stand shoulder-to-shoulder with some stranger and piss into some nasty hole. Then you go to wash your hands and there is never any soap or towels... just forget the whole thing.
It's so nice to be able to attend festivals, sporting events, & concerts without having to use those awful porta-potties. I can go to a movie... sit through the whole thing... and skip the long restroom lines afterwards. At work... I take one restroom break a day, and that's to change. On road trips... no stops. Out shopping... never have to bother with finding the bathroom at the stores or mall. Why interrupt your busy schedule with going potty? Use a diaper... get on with your day... and change when it is convienient.
There are so many situational advantages to diapers... somedays I'm suprised that more people don't use them. Call me crazy if you like... but that's how I see it.