I think it's pretty safe to say that there is one main reason why CC is still so popular:
It's free.
Arima said it already among other possible reasons, but I'm almost sure it's by far the main reason. A lot of young enthusiastic new developers simply don't have the money, esp. if they live in certain countries.
For me, the only reason to not buy C2 is that I'm still not able to develop reasonably, because all that fancy new tech just doesn't work on my pc. Software rendering with inconsistent framerates from 9 to 30 make it a hell if you're used to thousands of fps for the same game.
But money makes the world go 'round, if 'Cabaret' is right, and should be the main factor for most others.
Ashley: Don't underestimate that effect. C2 could be the only, completely bug-free, most powerful development software. But it isn't free. And the second place comfortable game making software ... is CC. This is not about C2 free or not free, I'm just stressing that people, who have the choice between a shiny horse that costs or a dusty donkey for free will very often prefer the last one. That's people's nature.