I think when publishers became mega billion-dollar companies churning out COD and AssCreed one year after the other while once cornerstone genres started disappearing or becoming real niche, space sims, immersive FPS/RPG sims, Isometric CRPG's, Point and Click Adventure games, RTS and RTT games either disappeared completely or became scarcer as gaming hit mainstream appeal.
Best years of gaming was 1997-2000, we had MechWarrior, Deus Ex, System Shock, Baldur's Gate, StarCraft, Close Combat 3, Wing Commander, Freespace, Planescape we were spoiled with choices in genre and high quality games. I gravitate towards AA and indie games more these days because I miss these genres.