Riding my DR350, I sometimes feel as if as if i'm intruding on nature, always worried about running into land owners, the po-po, etc. It just adds stress. NY is not very hospitable to dual sport riders.
On the mountainbike, I feel more at one with nature. The stealth quality is nice. Night riding is a blast! My 29er SS just rolls quietly along.
With my 3 little ones, including an 8 mo old, time constraints are always a factor as well. I can prepare and do an epic mtb ride and get home in 4 hrs. With the DR, it's an all day affair - packing, loading, fueling, unloading, riding til we're completely shot, reloading, unpacking, washing the bike. Granted, I still love those days but it gets harder to find the time due to familial obligations. I also get a real sense of accomplishment when I can clear obstacles and hills on the MTB that previously gave me a lot of trouble.