Two brass bushing are required per pulley before assembling into the der. I noticed the bushings have a loose fit into the cartridge bearing of the pulley. It seems like the as the pulley spins, the cartridge bearing would just glide over the bushings. In other words, there's not enough friction between the bushings and the inner race of the cartridge bearing to acually spin the cartridge bearing.
Perhaps when the chain is tensioned, it will create enough force to increase the friction between the bushing and allow the bearing to operate.
With shimano at least only the (guide) pulley closest to the cassette has deliberate side to side play. The lower (tension) pulley doesn't. That's why higher end shimano mechs use a cartridge bearing lower pulley and a ceramic bushing in the upper pulley. It's hard to engineer side to side play into a cartridge bearing pulley.
I tried Forté style pulleys once and never again. You can either fix them in position so they turn on the bearing and have poorer shifting. Or you can fit them loosely and inevitably they turn on the bushing instead of the bearing.