While I can't quite put how into words, this reminds me of the discussion about why more people do AH of Westeros on Ah.com than other fictional worlds (I think @zaffre was involved?) and how it having more long-term (if that's the right phrase) and wider-ranging world-building is part of that and that in turn in part being down to having rather more POVs.
I suppose spinoffs (if done well) are both the product and a cause of multiple POVs and more extensive world-building, in what can hopefully be a virtuous circle.