Weapons do get old and require maintains to remain useful.
It is not like the Russians haven’t used up a lot of their stock piles also.
You are missing the point. We used to stock, restock, and purge older stock of weapons in a regular and planned way. Our current military is under-equipped due to shipping our front line stock to the open sewer called ‘Ukraine’. Our weapons suppliers are not capable of backfilling what we we need at the rate we’re shipping it off to Ukraine, so, we are less lethal to defend ourselves and we lack stock for routine training. We are a weaker country.