My understanding/experience is that they eliminate the waist band in shorts/liners which can get uncomfortable on longer rides.

Believe me, I was in the same camp as you guys not too long ago.
Tried my 1st bib, & won't look back, they make riding that much better for me.
I have the padded shorts, but I only use them to train in, they don't feel as comfortable when riding any longer than as hour for me.