The reason why cosplaying as a certain character is different for everyone; but a rule for cosplaying as a character from an anime that ended is just plain wrong and stupid. It's like saying we can't cosplay as someone from a video game because everyone's progress in a video game is different. To me, both anime and video games are never considered the end.
I am not going to watch a new anime every season so just I can cosplay as a character because the show hasn't ended. That is a waste of time.
Besides, I love seeing my childhood and favorite characters cosplayed since it shows that it's still alive.
Chrome Dokuro [Katekyo Hitman REBORN!]
Rin [Togainu no Chi]
Lucina [Fire Emblem Awakening]