Why trailer wheel bearings need to be re-packed every year

After every season, I pull the wheel bearings off my trailer, clean them out and and re-pack them with fresh grease. This year, when I pulled the right hand wheel off the trailer, the seal was in perfect condition. The grease looked like the day it had been packed. There was no evidence of water infiltration. I started to wonder if I really needed to re-pack the bearings this year. When I pulled off the other wheel, it was a different story. From the color of the grease, it was immediately obvious that water had infiltrated the seal. The grease was milky white with rust mixed in. Letting that side go through the winter and into another season would have been a recipie for disaster. Each season, I put a few hundred miles on the trailer. I mostly use the local launch ramps around town, within a few miles of my home, but I do make a few trips to Newport, Point Judith and Charlestown each summer that rack up some highway miles. We've all seen too many boat trailers left along the side of the road due to a bearing failure to let this go. If you haven't pulled those bearings out yet, now is a perfect time to take care of them.
Regards,
Chuck