Vanilla TATW does lack many features that make a mod really worth to play and different from the original game. TATW has a very rudimentary recruitment system, simple buildings trees, no city diversification etc. Thanks to it's shiny-shiny policy though, the mod does attract tons of players, many of whom take interest in modding, but are unwilling to create a complete mod of their own. That is why there are so many submods for TATW, which implement all the thing, TATW is really missing.