It all began in 1987. MegaMan was born. Capcom found a gold mine that later turned into a stock crash.
In recent years MegaMan has fallen off the map. It may had been sooner than that. Seriously Megaman has taken a dive for the worst. With a shrinking fan base and no demand outside it, MegaMan is in big trouble.
In my opinion Capcom is to blame. Capcom is know for "don't fix something that isn't broken". I find that phase to be foolish. Nintendo always made changes with Super Mario. People will get bored playing the same thing over and over again. Capcom didn't really try that with Megaman. Look at the classic series. It is all side-scrolling. The MegaMan Battle Network series used the same battle system in every game except for one. Every MegaMan Zero game is side-scrolling. Every Megaman X game is side-scrolling except for one. MegaMan Legends was a bit different in 3D and offered something different.
Capcom never truly tried to improve MegaMan games. Capcom stuck with what sold for the first game and reused it too many times. That does not bring in fans. It may keep some fans loyal, but they will eventually demand for something different.