Because people need it. Once you think about a long time of quarantine, your mind will be on eating, sleeping and using the toilet. The corresponding items for each of these actions is food, bed, and toilet paper.
Back in the UK shoppers have emptied shelves of toilet paper across every supermarket in the country in panic over the virus. Pasta has also been cleared, preventing shoppers like me from purchasing anything. Why are people so selfish in times like these? We are all in this together, yet some think they have the right to stockpile certain goods preventing others from buying. During the wars the UK came together to help each other, but sadly todays generations only think about themselves.
It is understandable because they are worried about the shortage of some goods. People would not go panic buying if there was no emergency. The government should make sure an abundant supply of daily necessities is accessible. Also, the people affected should be quarantined to ensure the virus can be curbed as soon as possible.
I am in China, where there is no such behavior, partly because the government makes sure there are enough goods for all, and takes stiff action against profiteers. Chinese people have confidence in their government! I saw Aussies fighting in supermarkets over toilet rolls on TV, and the long queues in US shops and supermarkets with trolleys piled up full of toilet rolls and other goods.
Some panic buying in Canada as well, no need to and people are slowly realizing it.
This is the 'herd' effect. When you see others stockpiling, you feel compelled to do the same. Countless pictures on the media of empty shelves also spur buying frenzies for fear there won't be enough toilet paper.
I would stock up some frozen, dried and canned food. Why? Because these goods last for a while. But instead many are stocking up on toilet paper, detergent and other paper goods. Without food there is no need to go to the toilet. You will be amazed at how many people don't have a clue about what you need to survive.