Robin's whole raison d'etre is to be a gateway character into Batman's world. But that conflicts, over time, with long time readers and creators who want to see the character evolve beyond the sidekick role. As soon as Dick grew into Nightwing, then a precedence was set for each of his successors to do likewise. But, there always needs to be a Robin - the enduring popularity of the different incarnations of the character prove my point. So, along comes a new one to fill the proverbial "pixie boots" of the departing elder.
Each generation has its Robin. Tim is mine. I like Dick (phrasing!), Jason and Damien, but they're all lesser characters to me. But, everyone's got their own opinion, depending upon when they started reading comics, and which Robin they were exposed to first.
It is crazy that DC, for a while there, tried to claim that Batman had mentored four Robins in a 5 year period! Thankfully, that's kind of been quietly forgotten about with Rebirth.