agree with above posts.  unfortunately, we don't always have the luxury of choosing quality sealed bearings when we purchase equipment
agree w/pmsmechanic:  sealed bearings are cheaper to produce.  & just another throwaway item seems to be the way of manufacturing these days
as a footnote, i was glad to see that on a larger idler/tensioner pulley on my older Toyota pu that the sealed bearing itself is replaceable, a $15 press fit sealed bearing vs $175+ for the new pulley.
  
imho the best comprimise would be to have idler pulley bearings press fit replaceable.  doubt it will happen anytime soon.