UK panic buying - I'm puzzled

I don't understand the articles I see in the UK press of people buying so much that shelves are completely empty. It's not like supermarkets are not getting deliveries every day. So far, I've not heard of any food supply company say that they can't get their food to the end customer.

What puzzles me is the contrast of the current situation to the reaction of the Brexiters who, when told that if there was no deal in place when Brexit happened in full on 1 January 2020. the food that came from abroad (40% to 50% of the food that the UK needs) could well be held up in the docks for days and that fresh food would probably no longer be imported as that would spoil while waiting to cross the Channel, merely said, "That's OK. We don't need foreign food. We're too fat and overweight anyway. We could do with slimming down."

And now, when food supplies are not being interrupted by the current situation, they are stripping the supermarket shelves and leaving them completely bare. I don't understand it.

It'll be interesting to see what will happen on 1 January 2020. Bozo says that he will not ask for an extension for the Brexit negoations and that Brexit WILL happen on that date. We are certainly living in interesting times.