None of that has anything to do with why starcraft is popular, though. Starcraft has a long history of organized professional competition, and that's responsible for sustaining interest in the game.
So: money, gambling, ego bloating, greed, eye candy, narcotics?
At first people played Starcraft for the campaign, internet access in late 90s wasn't common enough for a game to thrive on mostly online multiplayer. And it was popular back then. And playing on LAN was more of "20 mins no rush" thing.