I have one myself, so I'm aware -- just didn't see that part of the post properly. Fixed my comment accordingly.

Anyway, the simple answer is that a full-frame mirrorless is for people who want the features you can't get in a DSLR, and also for the size and weight advantage. If you don't already have a bunch of lenses invested in some previous system, then it's pretty obvious why you'd choose a mirrorless when starting from scratch.