I think one of the big handicaps that Civ 5 modders face is the inability to modify much graphically. Most of the code issues can be resolved with DLL modding -- pretty much all of the total conversion fantasy mods have custom DLLs to help them circumvent some of the limitations that exist within the core game. However, they all run into the barrier that many of the graphical features of Civ simply cannot be modified -- you can't add new building styles, or terrain features, or new natural wonders. The best you can do is reskin existing terrain (I know Faerun does this to create the Underdark), but you still can't add new elements. You also can't add or even recolor visual effects like weapon attacks or animated features like Fallout.
There's also only a literal handful of graphical modders -- if you're talking about new fantasy unit models, you could probably count the number of people doing that for Civ 5 on one hand. Deliverator, Nomad or What, and Civitar are the major ones that come to mind, although a few people like Uruk and ispanets have contributed some models. I think I and Skajaquada may be the only ones that have converted any sci-fi models. There's at least a greater variety of historical models, but there's still only a handful of people actively working on them, and it's a major bottleneck even just for civ mods, much less a total conversion historical mod.
In my own efforts to convert various models to Civ 5, I have to look rather longingly at the variety of graphical elements that were available in Civ 4. Entire city styles, visual effects and animations... something like the Final Frontier mod would be impossible in Civ 5 without access to the graphics dll.
There are, of course, a variety of other factors as well. For all that I say DLL modding can at least circumvent many of the limitations built into the code, it's still a highly time-intensive process. I think that Civ 5 modding community is also rather smaller compared to the Civ 4 modding community -- there may be 3D modellers out there, but aside from the handful mentioned above, they aren't active here.
In the end, though, I enjoy the community we do have here. Compared to most gaming forums I've visited, it's nearly always been a rather positive place, where people think about how to make features they want to see in the game become a reality. Even if it's not a super-big community, that just means it has a cosy familiarity that can result in projects like The World According to Modders. It's one of my favorite places on the internet to hang out.
And it had G&K comp., just not BNW.
