The salient word here is 'sensible', aka altruistic. Why do you expect people to think of others? In a Utopian society, we will all be overwhelmingly 'nice', but several generations of people who had no need to look out for anyone else, other than their immediate families, has resulted in a 'me first, second, third...' attitude to everything, in this case anything available for sale. Unless and until a 'higher authority', ie the government, imposes restrictions on what people can buy, many people will simply take what is on offer, leaving nothing.
The measure of any society is how it looks after its vulnerable people, and unfortunately we, the British people, are falling somewhat short in the compassion stakes. I'm hopefully entirely wrong in this, but the current situation appears to show that taking anything/everything that one possibly can seems to be the default position.
Apart from that, how are things?