As others have mentioned, on Mumsnet there does seem to be some sort of competitive loner thing going on.
That's not unusual for a forum though. I know Mumsnet is hugely popular and lots of people are registered but often those that stick around and comment/start threads/become established are often going to be the more insular/introverted personality.
Forums do tend to attract those who may prefer an online life or may have little option due to their circumstances.
It puzzled me for a long time on here that even when people do have friends, they often seem an inconvenience. Their weddings, christenings, birthday parties etc are often a duty thing that people must endure. Imagine being asked to celebrate with people you are assumed to care about. The horror! 
I've never understood it because whilst I do have introverted tendencies at times and need time to retreat into myself, I love going out, going to parties and events.
I also love my friends and I think that what some call friendships are actually just friendly acquaintances.
It's really sad that some people say they're never able to make/keep friends.
I thought I was like that and found friendships really hard at school. I had a few good friends but we didn't really keep in touch when we left and I think that was me, I didn't put the effort it I just expected that things would continue as they had.
But then I found my tribe and I'm still friends with the same people 25 years later. We do all the things that some here find so weird or intolerable like group holidays, nights out, parties, day trips. We've got close relationships with the babies that have come along.
I've made other friends along the way but there's 6/7 women that I've known since my late teens that will always be there, I can't get rid of them.