Old games are competition for the new games. One of the major downsides of digital distribution is that old games don't really disappear any more, so every new game has to be significantly better to compete with the old games.
As it should be. A sequel should be as good as the previous game and more. All the maps, modes and more. Old games should not be seen as competition but as a measuring stick of the absolute minimum to succeed. They can't rest on their laurels and that comes part of the territory. Video games should not be made into a "product" its artistic entertainment. Does it mean an ever growing list of tasks? maybe, maybe not. But that's all irrelevant, its still no excuse for killing a game.
Honestly, i'm not sympathetic towards the AAA(A) industry. They're only as good as their last few games. I'm not going to blindly love bioware or ubisoft if they insist shovelling the same game whilst quality getting
worse each time. i'm not going to cry over their problems that they help create. Even less so when they kill my game to force me to get their next game.
I'll throw them a bone and say that the core mechanics don't have to always change, just refine the game mechanics, freshen with some new features, update the graphics, a new story and give me a setting i would play. Make the game like a holiday package or something. I'm a sucker for ubisoft open world games for the right price, but when you have a horrible reminder that you can brick my game(s) i'll think twice buying them.
I'll concede that a good game is might not always equal a good seller, just look at TTLG, but i blame that on marketing failure of the company rather then the consumer. They would gladly spend millions reminding us of well known franchises, trailers for trailers or trailers that do not reflective of the content. The millions should be spent on the new franchises and sold at a price that makes it work. Its perhaps why i gravitate more to Indie games for unique or fresh experiences.