And yet how many books has Sentry been in, including his own limited series? Now do Blue Marvel. It's not quite the same, even though everyone tries to convince us that it is. More writers and fans gravitate towards Sentry, as where Blue Marvel gets the "Do we have another Hyperion that we can use here?" treatment.
And just to be clear, I don't think retconning is the issue. No more than time-displaced characters are an issue, if the story is properly constructed.