CMSF didn't get anything in proportion to the previous CM games. While there is a lot of good stuff out there for CMSF it failed to reach anything like previous efforts.
The reasons for a lack of modern CM content are many I suspect. For one, those guys doing great work previously have been signed up by BF to do operations and missions for new games. Some, like the mad Russian, who made excellent CM scenarios have disappeared. And more tellingly, the system isn't as easy to do as it was formerly. Scenarios are much harder to design today than they were historically.
Compared to previously there is much less user made content and there are far fewer places to get that content, which is a shame. I thing CM has shifted from what it was before to a more single player experience. Also, there just seems to be a lot less people playing multi player out there, which always drove new scenarios and tournaments and stuff.
I'm not sure it's dying though, perhaps just refocusing a wee bit.