Like a lot of people I came here after googling something non-parenting related, probably something like “Best hoover for dog hair”. The search threw up a Mumsnet discussion on this topic. I clicked on it and ended up having a bit of a mooch around the wider forum.
Despite not being a parent, and not intending to have kids any time soon, I was attracted by the wide ranging discussion on a huge variety of threads, the humour, surprises, different points of view, life experiences, politics etc etc.
I lurked for ages before something came up that I felt compelled to post on (can’t remember what it was but probably someone asking for advice on something I had direct experience of). So I got myself an account and started tentatively posting and here I am a few years later a proper Mumsnet community member and daily visitor.
I expect that there are thousands of members who followed a similar route to Mumsnet. We did not feel like we were making a deliberate decision to join a parenting forum, just got sucked in by the general excellence of Mumsnet 
I have been a member for maybe 8 years (?) and am now a parent (had my first child 2 months ago). I still spend most of my time reading topics that have nothing to do with kids or families.
Does that help shed some light?