Yes. Is there any data to support that thesis, or are you just making stuff up from your own experiences?
Problem is, Space sims (Note the simulation part there?) are notoriously incompatible with anyone but a certain type of gamer. Same goes for realistic flight sims a la MS Flight Simulator or Falcon 4.0. And, you know, some people just don't like sci fi.
Granted, Space sims weren't always the kind of niche genre they are now, but what killed them were not a rising dislike of the genre, but a demographic shift in the gaming culture away from the PC and the nerdy corner into the cultural mainstream. That, more than anything, killed space sims as a big moneymaker.