Maintenance technician reported a ramp employee noticed smoke coming from the left main landing gear on push back from the gate. Maintenance crew investigated and found the #4 main landing gear bearing had failed.

Narrative

Aircraft X landed in ZZZ from ZZZ1. The ramp and flight crew failed to notice a failed wheel bearing condition at the gate. Since local policy prohibits maintenance personnel from performing routine maintenance walk around inspections on turns; there was no maintenance trained eyes on the aircraft. The aircraft was fueled; and passengers were boarded as normal. As the aircraft was being pushed back on to its next flight; a ramp employee noticed a what looked like smoke coming from the left main landing gear. The aircraft came back to the gate and maintenance was called to investigate. The maintenance crew determined severe bearing failure conditions and took the aircraft out of service. The aircraft was towed to my hangar on 3 MLG tires only. The gate maintenance crew was directed to remove the number 4 MLG tire for the ramp to move the plane.Remove the policy that restricts our maintenance professionals from performing walk around inspections at the gates on live flights. Wheel / tire / landing gear failures are becoming a common occurrence. This aircraft was very close to departing again with a severely damaged MLG. The next landing could have been catastrophic.