It probably has something to do with the a fact that when we got the trailer, either the manufacturer/dealer, over packed the bearings and our breaks & drums were covered in the grease. The manufacturer replaced all bearings/rotors/breaks when we took the trailer back to them, due to some major warranty issues.
No, I'm not joking in that he will pull the wheels/bearings and re-pack. Having had horse trailers/boat trailers, I remember doing them with my dad about every 5 years. Adding grease to the boat trailer, every time it was in the water...Horse trailer - adding once a year as it might get 1500 miles on it in a year.