That's true. There are alot of already diluted franchises out there, I won't argue. But with most of those you've listed they have a continuing and relevant story-line to them that begs them to create subsequent sequels, or each game is on its own with no connecting story-line.
I would accept another game from the Halo universe (like ODST, Reach), since the universe has its potential to spawn different characters and stories. But bringing back Masterchief when his story-line had a finality to it is just plain wrong.