Ah the good ol' days when farmers had 10+ kids.
Only 5 made it to adulthood due to diseases like measles, mumps, influenza, whooping cough etc. , poor and dangerous working conditions, and no healthcare. Of those 5 remaining, 1 of them died in childbirth, and 1 died in a random war and 3 went on to have kids of their own.
Russia has a long history of open storage at these sites. They also lost a ton of bunkers a few months ago at other sites. So they likely did not have much of an option, and they chose open store it at their "best defended" base.
I personally would bet that site was overstocked as it was likely the primary ammo dump by default. All of the newly manufactured missiles and shells going there directly from the factories.