The reason they look "brand new" is that you are cleaning and repacking them. As long as you maintain them, there is no reason to expect them to wear out.
Here is a quote from the e-Trailer website:
"With or without bearing buddies, we recommend repacking grease once a year. This not only provides fresh grease each year, but it is the perfect time to examine races and bearings. Check for discoloration from heat on the races. If you find dark spots or rings on the races, you should replace races and bearings. Also, run your fingernail along the race and if it snags, it is time to replace race and bearings. There is no need to replace bearings or races until you see cracks, heat marks, nicks, or any other sign of wear."
BTW, if you ever replace the bearings, it's vital that you replace the races too.
Jim
2016 Ford F350 Turbo Diesel SRW 4x4
2017 Grand Design Reflection 297RSTS
2013 Ford F350 Turbo Diesel SRW 4x4 (Destroyed by fire - 8/29/16)
2014 Grand Design Reflection 337RLS (Destroyed by fire - 8/29/16)