The thing is, there isn't really anywhere else to go.
Reddit has some subReddits that are close in tone and content to some of the boards on here, but are far far bigger than any of the MN board readership other than perhaps AIBU and so very very impersonal. The new TwasAllFields subReddit is a useful outlet for MN refugees for now, but I predict it will fizzle away in due course (or simply be the place where people post pictures of their dogs) because it isn't and can't be structured to replicate the various bits of MN, so if you want to get stuck into a good parking wars thread, you have to scroll past seventy billion "here is my dog" / recipe request / TV show discussion threads. Anyone looking for help on, say, a secondary school appeal or weaning would find it nigh impossible unless the thread happened to take off and get lots of upvotes.
I am still technically a NM member, and get emails from them every so often, but haven't been on there for literally years and cannot remember my log in details to de-reg. I have no interest in posting on that site, for various reasons.
I use some other online sites for niche things, but the great thing about MN is that I can do all my chatting about feminism, property porn, dress hunting, schools and Game of Thrones all in one place.