"Seasoning" the grill when new (or every few years) helps. I avoid wire brushes since they remove the seasoning layer and start the 'sticking" process anew. A stiff-bristled brush and, if necessary, a bit of river sand (or even coarse salt) does wonders. I avoid soaps and scouring compounds which almost inevitably adhere/become a part of the seasoning layer. Sugar? Cooking meat at high temps produces sugars also, simply not in the quantities generated by sugar-laden sauces and rubs.

An old geezer, I learned to cook on and in cast iron. Its common trait, a highly porous surface which needs seasoning and use and becomes easier to clean as time passes.