Why are so many great fighters of legend ignored?

Depends on which great fighters you're talking about. If you're talking about guys like Sonny Liston, Aaron Pryor, Ike Williams and Ezzard Charles, then I guess it's because a lot of these great fighters who were ignored, lacked "marketability" to not be forgotten.

Ignorance, short memory, indifference. Indulgence with the now which will soon become the past and also forgotten/ignored.

For example, many Pinoy boxing fans, including senior citizens are so agog with Manny Pacquiao that it seems Pancho Villa, Ceferino Garcia and Flash Elorde in the golden past and Luisito Espinosa as well as Gerry Penalosa just a generation back never existed.,

Joe Louis...................Now it's what Ghetto chump has the best rap signer to accompanying them to the ring. Obnoxious asses...........How do you spell yawn...."Broner".

Muhammed Ali? George Foreman? Joe Lewis? Who's ignoring them?

Cuz nobody cares. *yawn*