. . . why pay full-price if you're only going to use half of it?
. . .
I have one of these that has all sort of parts in there, including strap-buttons that aren't being used.
That's a big part of it--extra unnecessary expense, and having to keep unneeded parts around. I already have too many unneeded parts.
Plus, Schaller makes the strap locks that are stock on new Rickenbackers. They know there is a need for just the strap portion of the mechanism by people that already have the button end of things. I have three Rics with straplocks. I want to upgrade the mechanism on my straps. I shouldn't have to buy entire kits of which I will only get use out of half of it.