If everyone buys for a month at a time, it would be spread out over that month. With lockdowns, people bought more than usual, and everyone was trying to buy it

If everyone buys for a month at a time, it would be spread out over that month. With lockdowns, people bought more than usual, and everyone was trying to buy it at the same time rather than spread out. And then people heard about shortages and it just reinforced it - people who still had a month worth at home would throw another package in the care "just in case".