Quoted By:
Spiritual successors are the future of Pokemon.
Mark my words and screencap this.
Games are complicated to make, so most games eventually have companies made to manage them, which due to IP law, have absolute power over their IP.
Also, IP inevitably changes hands over time, until eventually an unscrupulous company gets their hands on it
They then inevitably try to make it sell with as little effort as possible, until its effectively dead.
Eventually people have enough, and they take what they legally can, and make spiritual successors to the original. Then the cycle begins again.
Jist is, the only thing that can stay high quality forever in gaming is the parts that can't be considered property, like the game mechanics themselves. Everything else has an effectively random lifespan.
TL;DR if you want to stay happy, don't get too invested into a single game.