Wheel Bearings. How often do they go bad?

The mechanic has shown me the bearings. It looks like the grease is almost gone and you can see rust starting to develop. Does this mean they’re running too hot? Or could there be an issue with sealing?

I actually misspoke in my initial post. The dealer replaced the bearings right out of the box. These lasted from 2004-2009. The same mechanic replaced the bearings in 8/09, 7/11, and now they’re going bad again. I hear the same familiar sound.

Could this be an issue wtih poor parts or could the mechanic do a poor job?

I frankly would do it myself if it didn’t required a press and removing the entire knuckle.