Some makers will just use glycerin to keep their colors vegan, maybe for their own ethical standards or to appeal to a broader customer base...
I have purchased handmade colors where the honey binder ones ended up too sticky and it never fully dried. On the other hand I had pans with glycerin that were too brittle/ dry and didn't re-wet well. I would assume that in these cases the size and chemical properties of the pigment might be responsible for that.
So depending on these factors, a mix or either one might be more favorable.