I know a bit about this, since I'm a member on RCTLounge for random NoLimits project posts.
Apparently those take ages to make. For one, the track is modeled by hand (I've been told many times that it's not NoLimits via CK), but that's only half of it. They then have to animate all of it by hand as well (the random shaking is caused by inaccuracies), which also takes a long time.
That's why people aren't just pumping out NoLimits-imported tracks into RCT3. Instead, a few people take a lot of their time to make standard models like this Junior Boomerang, where RCT3 players then download it as a CTR and assemble it in RCT3 in 5 big pieces and color it.
Trust me, I've asked lol...I've been wanting to do NoLimits models in RCT3 just for the sake of adding realism. I mean, I could even put a Newton track in RCT3, and they could adjust friction values to get a close match. It may not even be that close at all to perfect, but think of how much realism would be added to the game simply from having a track that doesn't look like absolute crap.
I'm still dumbstruck as to why they don't use NoLimits + CK to model tracks...it seems like that would be such a time-saving and smart idea. All I've gotten are extremely vague answers, mainly because the mainstream RCT3 players don't understand it much themselves...they just use it.
Now, I'm just like "whatever". It sounds like the people who know how to do it just don't know how to use NoLimits (though they should learn so their track doesn't have little jerks in it and so it's actually easier to build), and they don't want to tell anybody how to give it a try...they just want to keep to themselves for obvious reasons. But like I said, whatever. I've given up on it lol.