It may or may not be a contributing factor, but on the other hand there are plenty of other reasons. For example, other sites have since sprung up with offer a similar service with a far larger userbase; this site's demographic skews towards older people (and is relatively UK-centric at that); several sub-communities on AB seem to have just become smaller naturally anyway. On the latter, when I first joined this site it was specifically because of the Listener Crossword discussion, which regularly attracted 80-100 comments a decade ago but now seems to have dwindled to the teens -- I don't think I myself have posted there for about six years, so it's not entirely due to members moving on altogether, but as far as I'm aware there are basically as many Listener solvers today as there were 10 years back, so it's simply a change on what websites people use.
And, besides, some of the loudest moaners about aggressive moderation on AB remain among its most active!