I guess that now raises the question, is a $300 Million space game a niche market?
One of often-mentioned examples is Zune. In May 2008: "Since its launch in November 2006, the Zune has sold 2 million units."
Considering the SC sales can be considered around 1 million copies (used to be "about half of registered accounts" but these days I suspect it's less than that, as whales might be duping accounts for various reasons, from referral contest over grey market to "creating poor PC workers") - yes, SC is a niche market. Heck, Elite with its ~2.5M sold copies across platforms is still a niche genre these days, or Dead Cells as an indie game (niche rogue-lite) sold a bit over 1M copies over its lifetime.