I’ve been thinking about that. I spend a lot of time thinking about why groups of people do what they do and this one has me somewhat puzzled.
While I’m not sure how it got started I have an idea about how it continued. Once the toilet paper started running low people wanted to make sure they would have some so they ran out to buy it too, which is a least not disease related irrationality. So the hoarding keeps going disease relation or no disease relation.
For the record I’m not participating in that. I’ll use the water in the bowl, my hand, and wash my hands before I join the flock in this.
Now as for how it got started, I don’t know. I’ve to find examples of the early people hoarding it to see what they thought they were gaining. Maybe the toilet paper was just in someone’s field of view when the hoarding instinct clicked on.