...or a lack of reserve equipment.

In the German press, the Bundeswehr is pissed. For decades Germany has been intentially kept weak militarily by the west. You might remember from history class the last time German tanks rolled into Ukraine, but I digress. The Bundeswehr is pissed because they don't have a huge surplus of well-maintained modern military equipment sitting around. If they send much "good stuff" to Ukraine, they will be sending weakening their own military.

The US has been on a "just in time" profit-driven path for 40 years. That includes military equipment. Our weapons are built by contractors. They only manufacture when they have a contract. Ukraine has burnt through years (IIRC in some cases decades) of weapons stockpiles in months. It will take years to ramp up production. For just one example that is why we are sending 105 mm mortars instead of 155 now. We don't have anymore 155, and are having trouble finding stockpiles around the world.

Russia arms are made by the government. They have kept huge stockpiles of weapons. They kept most of their factories, even if some are semi-mothballed. Are those arms and armaments ready to go? No. Up to date? No. 10-50x faster to get up to date and/or on the battlefield than building new? Yes.

The Russians are captialists, but not like the US. They are much more social democrats - except for elections! - than we are. The big ticket items we have privatized fully or mostly: health care, school, the military, they have kept public. So when an authoritarian leader like Putin says, "Make more tanks!" there is not as big of a lag as we have with the whole legislative procurement process.

It is not that I want to live in Russia, but at this point in time (2023 and not 1943), they have an advantage over the west, and particularly the US, in ramping up the military.