Why aren't sealed hub bearings common place? Loose hub bearings may be cheaper to mass produce, but why wouldn't sealed hub bearings be one of the first upgrades to a bike?  It seems that most of us choose loose bearings.  I'm thinking of putting in a set of sealed bearings front and back and be done with it.
Cone, ball and cup aka traditional wheel bearings are the simplest and cheapest expression of wheel bearings. Simple to manufacture, easy to maintain and repair with the simplest tools and a handful of standard parts that have been around for more than a century in the remotest locations. And the wheel will even turn after emergency repair when, say, one bearing ball is missing, while a toast sealed bearing means a break-down.
Sealed bearings require high precision manufacturing, logistics &amp; stock-keeping, special tools and trained mechanics.