I've always been intrigued by that aspect of a book filled with contenders, but the second they become a champ, they're out, or relegated to guest appearances. It's completely counter to the way these things work now, where nearly every new Justice League iteration, Batman at least shows up, because his popularity makes him a selling point.
Now obviously this isn't universal - many teams like the contemporary JSA, the Legion of Super-Heroes, the All-Star Squadron, etc. tend not to have many or any characters who have their own book outside the team! But the Big Teams, the Justice Leagues - which the JSA was at the time - generally has only a few members, like J'onn J'onzz or Cyborg, who struggle to keep a regular title.
I mean I guess all that goes without saying but heck if I didn't decide to up and say it anyway for some reason.