23 years ago - Jason Todd is born to poor parents in Gotham City.
13 years ago - 10-year-old Jason Todd's mother leaves his father. Jason is told that she died.
9 years ago - 14-year-old Jason Todd's father is killed by Two-Face, he helps Batman catch him. When Dick Grayson is fired, Jason becomes the new Robin.
8 years ago - 15-years-ago Jason Todd, exhibiting recklessness and violence as Robin is pulled from active duty. He leaves to find his mother, discovers that she is working with the Joker, and is killed.
Jason is a divisive idea, because his career as the Red Hood, while extremely popular, is one of the most glaring examples of retroactive rewrites in modern comics. To paraphrase Dickens, Jason Todd was dead to begin with. It's an understood, well-trod part of the mythology, and to deliberately bring him back undermines the existing narrative. After a certain amount of time, a character is simply dead.
Moreover, while the character might be popular, we continue to insist that the most important task for any on Batman's supporting characters is to make Batman a better character. Jason Todd's death is one of the greatest moments in the history of Batman, and the omnipresent specter of Batman's single greatest failure is by fat the best contribution any supporting character has made the the Batman mythos. Bringing Jason back robs the story of that.
We've done some work to make sure that the character of the Red Hood still exists by putting someone else under the mask, which might seem to be diminishing Jason Todd's role in the mythology, but make no mistake, he is one of the single most important parts of Batman's story.