In my experience, the person ordering something a bit drippy like a passanda will tend to be a non-sharer, who will be frightened of trying my SPICEWARRIOR main anyway. I think it’s ok in a group to have some people sharing, and some not. Some people also have specific dietary requirements/ are veggie/vegan.
And then you just have the non-sharers just BECAUSE. my mum doesn’t like sharing. it’s like a family joke now LESLEY DOESN’T SHARE. We’re doing xmas shopping and dinner next thurs and I’ve booked us into a seafood restaurant which does small plates and I’m fully prepared for her not wanting to share the scallops.