Unity the straw that broke the cycle. http://www.bit-tech.net/news/gaming/2016/02/12/no-assassins-creed-2016/1
Because we live in a world driven by capitalism. Because Ubisoft is owned by shareholders who demand returns. Because milking customers using a big franchise is a good way of making money. Make no mistake. The shareholders that make these decisions do so based purely on the promise of a monetary return. This decision is no different and is not because they want to treat fans to higher quality or because they feel bad for letting the quality slip. It's because they've looked at the cost of the reputation damage to the IP and to Ubisoft and they've calculated that the loss in sales from not releasing a product this year is cheaper in the long run than destroying the IP outright. It's all money. I'd bet the majority of shareholders barely have any idea of what an AC game is. They don't give a flying fart as long as their dividends keep rolling in.
Not really, for all it's faults Call of Duty is at least a functional game every twelve months. AC can't even manage that.