Because your own elements have only one certain radius at the beginning, and another at the end. It probably wont fit in someone elses track aswell as it did in yours. Also theres no point in uploading stuff like that, we share tracks, if you want other people to help with trackwork, then you get a joint project going. By uploading elements, you get a load of noobs just making total rides out of elements made by people such as Real, Hansixx, and Kev etc.