Which brings me to my next point, which is that the community aspect of StarCraft is a huge part of why it remained popular for so long. As previously mentioned, there were hackers and programmers developing awesome tools that helped the scene, but also there were map makers which were essential in keeping the game balanced. One little known fact about StarCraft is that the last balance patch released by Blizzard was in 2001, at the early beginnings of the pro scene. After that, the game was kept fresh and balanced by community map makers.
Combine that with people who created websites where you could follow news about Korean pro scene (TeamLiquid has its roots here), talk with other people about StarCraft, and other people who organized tournaments and did everything else; and you get a formula which almost ensures the longetivity of the game. I wouldn't be surprised if there are people playing and following this game in 20 years time. I know I'll be one of them.
[0] - https://github.com/TheEngineeringBay/Awesome-Broodwar-Resour...