Well, to produce a dry or lightly lubed beraring with four extra parts that represent wasted time and material, doesn’t make much sense. I suppose the answer could be that yoyo bearings are such a small a piece of the bearing consumption pie, that it’s more cost effective to produce them without making this “special order” change. This doesn’t really make sense to me, as (as persson has pointed out) the shapes of the outer races along with shipping dry, are special order items. If shields serve no purpose other than “that’s the way we do it.”, then why not order them shieldless as well, and save on costs?
Also, there are bearings that come without shields. My hybrid Buddas came without them. This leads me to believe that there is some truth to what Schnayke is saying, but it’s not the whole story, and there is even debate on this issue among yoyo and yoyo bearing “manufacturers”.
Regardless, I’ve had a better experience with the shields in place, while others have had a better experience with them removed. Seems to be one of those personal choices…