Unless the OP is being sarcastic, the honest answer is: A LOT of things.

Even if you just want to point at something like Madden, there is still ZERO reason in today's modern gaming climate, to develop and release a WHOLE NEW game every single fucking year. It would make far more sense, development cost-wise and fan-wise, to develop and release a new Madden, say, once every 3-4 years, with updated engine, graphics, features, etc., and in the years in between, simply release updated rosters and whatnot every off-season.

But for other shit, like Call of Duty, or Assassin's Creed, or whatever else, say, the way Guitar Hero or Tony Hawk used to be, that shit literally got ridiculous. It's just trying to get more money from customers with half-baked bullshit. It floods the market with a franchise that DOESN'T need that many entries. There is a valid argument to be made that even Nintendo overuses the Mario characters, for sure. But the difference there, is that Nintendo only releases a new MAIN Mario game, or even 2D "New Super Mario" style game, every few years (on average). The other shit they slap his face on, at the very least, is widely varied stuff, whether it's Mario Party, or some Mario Sports title, or whatever. It still isn't releasing ANOTHER Call of Duty shooter every single year.

It is most certainly a bad thing, and a phenomenon that needs to stop. Problem is, just like Hollywood continuing to make and release shitty, pointless reboots and remakes and sequels, and adaptations of garbage no one asked for like Battleship (as one absurd example among many), these game publishers aren't going to change their ways until gamers stop buying this trash by the millions. As long as they think that's what people want, and so long as they see that is what is making them money, then they will happily continue.

Nothing.

I wish we had monthly franchises.