Generational improvements become smaller and smaller as a technology improves, giving consumers less reason to upgrade with each iteration. That leads to price drops to stimulate sales as mentioned, which causes more of the potential market to buy in, which in turn, leads to fewer people in need of an upgrade the next generation. Eventually the market is simply saturated, and prices have fallen as far as they can to maintain profitability, and everyone who was going to buy, already has.
Then you either need to open up new markets, or substantially improve the technology.