Hmm, I did make track from scratch in 3 hours and yes it is pile of crap. I don't see really much point in conversions as you still need to do almost same amount of work, only amount of research will be different, all mapping and texturing is needed to do again which is quite most of the work, modelling is not so big task, with conversion there can be even more work with textures than with scratch made track so really, why to do conversion?
I think that these tracks are only result of beta testing of that track editor tool and there is different team doing this beta testing and track making and different team working on bug fixes and track editor.
I kind of like from that game even it has some problems, looking forward that time when there is some cars with roof.