The problem is that processing centers are overloaded. As a result, more and more boxes and parcels pile up. Sometimes it gets even more ridiculous, like recently in Moscow, when some boxes caught fire.
Besides, the whole processing system is so ineffective, that you could send a box from China to Far Eastern Russia (relatively small distance), which would first land to be processed in Moscow (great distance) and then be sent back to Far East.
Also, there is a queueing problem in the goddamn post offices, I won't even get started on that, it is so infuriating.