Starcraft community is slowly declining, Command and Conquer is getting EAed, Age of Empires got killed by Microsoft, Company of Heroes is too much based on luck and many times your units do what they please, Total War isn't that popular.
I guess unless a dev comes out with another good RTS, then this genre will probably die.
I do think it is dying. One of the major reasons is that publishers who invest in AAA titles want to see them go multiplatform, since that is where the money is. The genres that have a control scheme that does not translate well to consoles get the short end of the stick.
Currently, there are only a handful of developers that can still make a PC platform specific AAA title like Starcraft II.
But that is not the only reason though. MOBAs have the same problem but they are tremendously popular.
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