That seems more like it's the result of how the rules for THAT particular show were written.
Even for small guild shows, I'd be surprised if they didn't require the LA name to be listed. However, there might not be a separate category for Duo quilts.
But if the quilting you're referring to is an all-over pattern, on quilt after quilt after quilt, like a panto, it could be the LA's in that area do that sort of work. Or it could be a the result of budget constraints - quilter needs it quilted by LA, but can't/doesn't want to spring for more creative, free-motion quilting.
If I think back to when I first started (11-12 years ago), if you looked at all the quilts in my little bee group, we all had the Oriental Illusions as the panto, done by the same LA quilter.
This was a decade ago, and we were ALL on a learning curve, including the LA. Now, we all have our quilts custom/creatively quilted.
Maybe it's the same for the ones you saw. Newer quilters who might not be aware of the possibilities available.