How often do front wheel bearings need to be changed?

Sounds like both fronts changed? How many is the low miles? If car sits for long periods of time the bearing surfaces can get flat spots. Is rare but have seen it once when I took apart a set of old front bearings in a hub off of a fwd vehicle. Sometimes have also heard of low mileage vehicle that had been in high water and contaminated the bearings. Lots of possibilities.