Uncle Dave-O explained what I was trying to say, and probably did a better job.

I think it's not exactly true that "the superdelegate system was adopted some time ago," so much as that these party stalwarts were always included in the convention, but only began being called "superdelegates" as their numbers started to decline.

For many years, they were the only delegates, and it's only more recently that slates of delegates determined by primary elections and caucuses have been admitted and gradually become the majority of delegates. It's only in the light of this historical development that the party insiders who have always been part of the process have declined in numbers and been given a new description, "superdelegate."