That's right. There ARE reasons FFH2 and Rhyes MIGHT have been more popular than C2C is today but I think you've mislabeled the cause, ls612.
These, I think, are the more applicable causes:
1) Those mods were in their peak when there wasn't a massively competing CivV. Considering how much less overall activity there is in the Civ IV forum in comparison to how things were rolling pre-civV, our success rate here in C2C is astonishing!
2) Those two mods had a vastly different way to go about playing civ from the base game. Particularly FFH2 being fantasy, it was sure to have the ability to capture a HUGE fantasy fanbase that even Vanilla Civ only somewhat inspired (just enough to purchase and play a game or two) until this was made available to them.
3) Keeping things simple, almost annoyingly so, they were able to have a fairly complete picture in a fairly short amount of time. However, honestly, if FFH2 had not had such a constrained minimalistic approach, I probably would've taken all my efforts there rather than C2C.
But while it inspired me with great expansive ideas, it also frustrated me in how it went to such a shallow level with those ideas and really eliminated the point of utilizing those ideas in the game at all by approaching them with such basic implementation. At the same time, they did have those things quickly done and polished out in the large scale scheme of their mod so they were able to do what they did in a smaller frame of time and then tweak for balance and wrap things up.
C2C, however, is the pinnacle of all diversity, influenced by all modding that has ever been done for Civ IV, including elements of both of those mods, but taken to the next level I think most of wish those mods had taken it to. It's a work in progress and will continue to be for a long time. FFH2 and Rhyes (even AND) were able to get to a point where the primary developer said... OK. We're pretty much there.
Seriously, if C2C were in its current state, competing side by side with Rhyes and FFH at their peak... do you think there'd be much of a challenge to C2C now? Sure we wouldn't have a monopoly or anything (we don't now) as there's always those who gravitate towards one thing or another, but in terms of pure quality, we're right up there with them imo. And getting closer and closer and preparing to surpass entirely. Unfortunately, as we go about doing this, CivIV itself begins to appear more and more archaic to those who've moved on to CivV. I loved Civ II but looking at it now, even though they'd achieved the multi-maps and so many things we're striving for here, the rustic quality is just .... toooo rustic. Perhaps the sad thing is that by the time we're where we want to be with this, Civ IV will be the same way entirely. But that's when we take our GAME structure and migrate it to something more... high speed and graphically intense.