I wonder why manufacturers don't use more roller linkages? I assume it is because of the expense, but the rollers sure seems to work better.
Could be. It could also be for the same reason they would use sharp-ended adjusting screws on sliding, screw-against-cork bumpers:
1. They haven't learned about friction yet, and no-one there actually plays the instrument themselves at all, i.e., they aren't aware of the problem.
2. They know about the problem, but they don't care. They found that they are able to sell the instrument to those who haven't learned about friction yet, and don't play the instrument well enough to be aware of the problem
As mysterious as that question is, I'm more curious about how WWBW could justify stocking/selling something in this condition.