It happens to a lot of games, really. Fortunately the internet has made it more difficult for games to fade and be forgotten since their fanbases tend to keep them alive through mods, forums, youtube videos, FAQS, etc. The Earth 2150 series is an example: the first few games were great and innovative during their time (only Warzone 2100 had done that type of design-deploy-destroy before them), the graphics were great, and the campaign and plot certainly were different from the norm. However after the mediocre Earth 2160 was released, interest in the game just died outright.
The average RTS player, even some of the experienced ones may have absolutely no idea the game ever existed. Yet, it's still a fond memory for some of us, and some devout fans are still trying to support it with mods, balance patches, translation fixes, etc.
Would you believe I never fully watched the original Indiana Jones trilogy? I gotta correct that someday.