Just think how much worse it would be this week if the 'planners' hadn't bough their extra supplies gradually over the past few weeks!
Their foreward planning didn't empty the shelves - the supermarkets were able to restock their shelves as normal, so it had little, if any, effect on others.
It's the last-minute panickers who do that, suddenly running around like headless chickens, grabbing whatever they can from the shelves.
Meanwhile, I imagine that most planners are now, very sensibly, avoiding this frenzied supermarket sweep, meaning that their actions have actually reduced their impact on the current situation, not added to it!