Nobody in this video is buying an excessive amount of toilet paper. Everybody is buying only a single unit of the smallest size that Costco sells.
If you are a Costco shopping, then you tend to buy in bulk. You might buy toilet paper only once every few months, even for a large family. Unless you restocked in the last couple weeks, you'll likely get another package now.
So that's what you see among Costco shoppers: people buying that next unit of toilet paper.
How about all those pictures of empty shelves in other stores where toilet paper used to be. It's likely simply a supply chain and retail issue. Retailers allocate shelf space according to the value of the $$$$ of the item being sold.
Toilet paper is bulky and cheap. Thus, the supply at a retailer will be likely be more limited than other goods. If preparing to be holed up at home for a months, it's a good chance that due to simple economics of the situation, it's one of the first thing stores run out of.
The #COVIDー19 is full of stories about other people are being extremely stupid. I'm not sure they are. I think instead it's those writing/reading the stories who don't understand the reasonable explanation behind the seemingly unreasonable behavior.
