Deactivating the BIG Guns?

I went past a VFW in another town that one of my friends is a member of
and noticed that their WWII artillery piece (a small one) had the bore
recently plugged with concrete. I was told that it had been there for 30+
years and had been deactivated in "other ways" but that this additional
measure of plugging the bore had just happened last year.

I'm just wondering if this was something that was mistakenly left out of the
proper past procedure, or if this was just something new for no particular
reason?

Bores don't have to be plugged. The breech has to have a section removed by torch or saw, though. Don't know the size (fraction) of the breech needing to be removed, but the BATFE could tell you.

My guess is to prevent vandalism. I knew some folks in college who liked to pour paint down the barrel of a particular cannon. People would also throw trash down there, etc.