They didn’t develop an identity outside of being Supergirl, Superboy, Robin etc. this always placed them in a precarious situation because new creators were always going to come along and want to create their new generation of sidekicks. I’ve always thought that the sidekicks that survived were the ones that were able to evolve into their own identity outside of the sidekick moniker.
Nightwing Red Hood, Arsenal etc. The ones that are to predicated on being the sidekick are the ones that ultimately struggle. In short...
You’re not going to be Robin forever. So you might as well start building some ground work for the character so when they have to give up the mantle, they have something to grow into.