Because of high losses: Russia's army sends soldiers to the front with cheap Chinese carts. Russia keeps losing important combat vehicles in the Ukraine war.
The supplies are now said to be particularly dangerous for their own soldiers. The vehicles should be cheap and quick to procure, but also not very robust in wartime. They can be destroyed by Ukrainian mines, drones, rockets and artillery without much problem. Even well-placed rifle shots could be enough to temporarily disable the vehicle. Russian military’s loss of 200 armored personnel carriers between February 14 and March 14 is a problem.