2006 Chevrolet Equinox Ve Had Vehicle 3 Years Really Until Recently

I've had my vehicle for 3 years and have not really had a problem with it until recently. I've noticed over the last year and a half things going wrong with my vehicle. My passenger side motor to my window quit working along with the speaker. Then my pump to the back fluid box went out but here recently I noticed a noise coming from underneath. My family thought I was just hearing things and it was nothing to worry about. Well needless to say it was my carrier bearing that went bed. My question is what causes the carrier bearings to go bad in a 2006 Chevrolet Equinox?