Statistical referencing based on previous discussions on the forum and other sites like reddit and various gaming sites around the health of various games and active player bases.
Feel free to do some research, or just keep arguing with a smug internet person, up to you
However in regards to the OP. Space games in general are in a decent spot IMO. there are a few really interesting one coming out soonish as well (Avorian, Starbase for example) but there has also been some lost like Hellion.... Space engineers and kerbal also have their niche playerbase as well.
Space games are more than just the 3 commented upon in the OP