Except the difference with those two cases is that Guitar Hero actually did have quality, but essentially was usurped almost immediately by Rock Band which added more instruments and updated their song lists through DLC, rather than Activision doing Expansions of old. For GH, it was simply a matter of not adapting fast enough along with Rhythm games just really being a fad if anything.
Tony Hawk, usurped by Skate, and the fact that...skating just got less and less popular as the years went on. I mean, the most well known skaters outside of Hawk these days are Dyrdek, Sheckler, Margera and Koston and only one of them is due to their actual ability to skate (Koston if you haven't figured it out). TH would've only went so long anyway, even without Activision running it into the ground or if it was the best skate simulator on the market.
Yeah, if shooters go dead, so does Activision. But since COD is essentially carrying the torch, it will be ITS death that causes the genre to go. Not because of the quality so much, but because COD has been such a surefire success, its death will scare all other companies from actually trying to make one themselves. But by COD existing, quality of the games or not, it allows other companies to do what they want to do in their shooters without too much pressure in being the next big Blockbuster, unless you want to be stupid and try to call out COD on it, in which case you probably screwed yourself no matter the end result of your game.
