I've not used additive manufacturing, but have used NC manufacturing a lot. The initial file you are getting from Creo is just a geometry file. In order for your 3D build machine to use that data, it has to be processed in a fashion that your machine will understand. There are many 3D build machines out there, all with their own requirements for code format, prep codes, etc. Thus, you have to use the specific post-processing software provided with your machine to convert that 3MF file into slices and ultimately the G-code that drives the machine. Creo doesn't do that - it just gives you the geometry.
Even with the NC programming funcitonality, what Creo puts out is a "universal" intermediate program file, that then has to be post-processed to be useful for the specific machine it is intended for. It's a two-step process and probably always will be. There are always new machines coming out with their own specific coding requirements.
