The End of Path of Stars

In all seriousness, the readers get attached to Grey Wing because we've pretty much been seeing his point of view from his teenage years till his death. This has barely happened with the other characters. We saw Firestar and loved him in the original series, but after that, nobody could care what happened or what he was feeling. Same goes for every other main character for each arcs.

But for Dawn of the Clans, it was the first time we saw the POV of a character from young to death, we never strayed away from Grey Wings development, that's why people get emotionally attached. If Grey Wing stopped being the main character and died like 2 or 3 arcs later, we wouldn't be as torn up as we did right now.

This generally applies, if he entire Warriors Saga was written in Firestars POV, then maybe his death in the last hope would've churned more of an emotional response.