I just hate shaving. I used to shave my beard in the summer, when it does get a bit scratchy from heat and sweat at times, but the last few years don't even bother with that. Also, the amount saved in razor blades and shaving cream adds up over time. (Weighed against one electric beard trimmer that costs $20 and lasts many years.)
There can always be legit psychological issues involved in appearance choices. Plus some folks follow trends. Me, I just hate shaving.
P.S. When I first grew my beard, at 23, people stared at me funny, since younger guys almost never had beards back then. (late '80s) Today you see high school kids with beards. Go figure.