To me, it is a forum, not a social network (although both have many in common), but there's no reason for that to be required at signup. It makes more sense for it to be added if users want to in their own profile page.
One of the reasons some websites grow fast (DigitalOcean, Quora, etc..) is because they have a streamline signup page, asking for just username and passwords. Other details can be added later if user wants to, inside their own profilepage.
I hope that XenForo team would make this feature not shown up by default at registration in the next version. It'll boost signups, benefiting site owners and XenForo global statistics (market share) in general.