Let's assume you create a Preset of a Distortion in Module A and that would hypothetically include an assignment of Effect Button III. Now you move to another Rig and load this Preset into Module C. In this Rig the Effect Button III is already assigned to Delay and Reverb. What should now happen?
Should the assignment of Delay and Reverb be overwritten? But this might come as a surprise. What, if you don't want that?
Should the assignment of the Distortion be added beside Delay and Reverb? So, Effect Button III would now switch Delay, Reverb ... and Distortion, but you just see Delay and Reverb, as the third assignment is "hidden". Another potential surprise. What if the Effect Button III had already four assignments? Should the first or the fourth be overwritten now? Or should the new assignment we waved?
If you would load such a Preset, it would be practically unpredictable, what happens. I think, this is a rathole. That's why the assignments are not included in the Presets.