I think TC is daunting for a lot of people, mainly because you're making 3 (or more) small maps inside one large map, which can get frustrating to juggle about with.
The same could be said of 3 stage A/D maps.
That said, a lot more balancing is required; as often, stages arn't symetrical (or atleast for the only official TC map so far, but thinking of other maps like meridian also).
I had initailly thought TC to be rather simple, but apparently even Booj has had difficulties with the game logics. So maybe i'm just too naive to realise how complicated the setup really is. Or maybe he just hasn't looked at it
properly yet.
It is most certainly a project of projects. But many beginner mappers have not been intimmidated by large projects, such as Eerieone and his Cashworks, and others undertaking payload and now PLR maps, with little to no experience.