An attribute shared by almost all superheroes belonging to the big two is that they do not age, do not grow up, and do not reach their final goal. If a hero aged into a senior citizen after defeating all of their foes, that would hardly make for an engaging, ongoing story. Heroes need to stay in their physical prime and maintain a recognizable costume in order to be a consistently reader-friendly, marketable character. However, Dick Grayson has defied all of those tropes to reach the pinnacle of his superhero career: he became Batman.
Watching Dick start as an orphaned acrobat who donned the Robin costume was like watching your little brother play in his first little league game. Seeing him grow into a teenager as Nightwingwhere he protected his own city was like sending him off to college. And witnessing him take up the Bat-mantle and wield it with as much authority and cunning as its previous owner, well, it’s enough to bring a tear to your eye.
A bright young hero growing into a darker entity, learning from the rest of the Bat-family, and stepping up to fill his mentor’s boots to complete a full character arc is unheard of in mainstream superhero comics. Given how most of us grew up along with him, Dick has a special place in our hearts.