Life is too short to race to the finish!
That's not the reason people like me would rather paddle than camp. You're likely thinking of an A-to-B river trip, where there's no place to go other than downstream to the takeout.
In contrast, on a big lake or a series of interconnected lakes with many routes, the let's-keep-paddling person (like me) may want to explore the other shore, those islands out there, the connecting streams, and some short-portage-away lakes that are not on the trip itinerary -- which itinerary is usually calibrated to the slowest paddlers in a group. I have no interest in preparing meals, cooking, processing wood or washing dishes, because those are the things I do every day of my life when I'm NOT PADDLING -- the daily routine I'm escaping FROM.
By spending as little time in camp as possible, I'm not racing; rather, at my often lollygagging pace, I'm enjoying additional paddle time to watery places that the rest of the group will never see on their route. As they sit and putz around, wasting valuable vacation time (in my opinion), under a bunch of trees in a small space with a lot of bugs . . . and tolerating in close quarters each other's annoying human habits, like gabbing and farting and drinking, which I also prefer to vacation from.
I can't speak for why others may not like a group pace or milieu, but as I said, other than day trips or simple one-route A-to-B river trips, I long ago decided that going solo is much simpler, and also provides the extemporaneous flexibility that I value far, far more than structured group activity.