I also think the stupid race for multiplayer & eSport killed the RTS genre.
But I'm not surprised they have more players because MP game can't survive without a minimal mass of player, so few survives and get all the players.
Whereas SP games can be appreciated as long as the sales pay the development.

I'd say the fundamental blocker that keep RTS dead is our inability to accept AI/NPC in RTS the way we accept them in FPS.
Just like a lone player don't make a team, a lone commander can't micromanage a bazillion of units.
But if in FPS having bots only make you more important and is not your fault there's a lack of human players, in RTS wanting smart units is treated like an insult, as if your power as a strategist was in your APM count.

Playing against bot is shameful because they are ratarded and need economic win/cheat to have a chance
And because of that developers don't even bother spending money on AI, keeping the bot retarded.