Mechanical picking has been too slow. It's not a problem with the robot mechanics. Here's 300 picks/minute from 2012.[1] The parts are all the same, so the vision problem is simple.

But picking arbitrary objects from fulfillment bins is still running at a few picks per minute.[2] As the speed picks up, humans become less necessary.

[1] https://www.youtube.com/watch?v=6RKXVefE98w

[2] https://www.youtube.com/watch?v=2X4CU3jmw-g