Because no one wants to beat a dead cow. Not saying these franchises were dead. But it's better to remember a franchise as being iconic and amazing and loving to see a return of it (which they do by making HD collections) Instead of only stopping once everyone is sick of it.
Microsoft does not seem to care about that which is why Gears is still going. Epic don't want to make them anymore, Judgement was mediocre so they just pawned it off to another developer to keep the series going. Halo will get there as well eventually it'll just take longer, but even that is getting some series fatigue.
There's only 2 races: White and 'Political Agenda'
2 Genders: Male and 'Political Agenda'
2 Hairstyles for female characters: Long and 'Political Agenda'
2 Sexualities: Straight and 'Political Agenda'
