I can't see where a person being stuck at home would increase the amount needed, but only the location it was needed at. And generally, all commercial sales are bound by contract, so until said contract has been fulfilled that amount wasn't and isn't available for any other market segment. If there's no other hidden force involved, the main reason for this shortage is hoarding, and to a lesser degree the methods of profuction and distribution we have in place for it and similar commodities. But mostly hoarding. Now I'll freely admit to buying a month's worth instead of a week's worth which I don't feel is hoarding, but it is 4x what I'd usually buy, and of that some was gifted to others so not really 4x when you take that into account. The real problem was (and is) the panicky paranoid idiots who have (or at least had) more money than brains and went out buying a shopping cart full of it. Along with the stores who sold it to them. Those stores surely saw the sales trend, but instead of limiting quantities sold per customer they simply ordered more, thus emptying their warehouses quickly.
As a aside, here in the US the larger 'chain' grocers inventory management at store level is done automatically now. At every daily shelf restocking the new goods are scanned, and the store computer adds those numbers to the next order- no more and no less- with the store manager now serving mostly as their HR fepartment to be sure there's enough workers when they're needed. Everything else is automated and so rigidly administered that it is nearly impossible for the store manager to get you a non-stocked item or to change any quantities which the system orders. They can't impose limits, offer deals, or change where items are stocked on the shelves without specific permission from higher up, and that permission isn't going to be forthcoming from someone who will be held responsible for any mistakes leading to losses, but who can cover their behind with the excuse that they followed the system as they were supposed to so any problems were not their fault. TBH, nost of the work being done could be done equally well with trained monkeys which is the corporate intention, since that kind of worker is cheaper to hire than one with a functioning brain. For the goal of maximizing corporate profits it works well, but it has little benefit to anyone below that level.
Phil