The HG was being disbanded, the guns weren’t suitable for frontline British troops, so the decision was made to melt them down for war production. Remember we needed every scrap of metal we needed, from old guns to metal fences.
I am not saying its right, just passing on the history.
In the U.S., a lot of historic old locomotives were melted down after Pearl Harbor.
In Britain, cannon dating from Napoleonic times went into the smelter. I would have thought, though, that if the Home Guard was being disbanded that the need for scrap metal wasn’t as dire in 1944 as in 1940.
Hindsight.....