Before the scarcity panic started, I bought a jug of sanitizer because I was fixing the plumbing that weekend and the water was out. That stuff will last forever because once I fixed the pipe, we wash our hands like normal people.
My wife's got a friend in Australia, which is about a week ahead of the US in the future (a joke for another time) and they already had the TP scarcity so she sent me to the store to grab a pack. The next day, the hoarders hit, and I haven't seen TP on the shelves since in Houston. A friend who works at HEB scored me another pack last week.
As to why it's scarce? I assume two factors started it: intent to price gouge and desire to quarantine for a long time. With no limits in place, those people emptied the stores.
My agent at HEB then explained why the problem continues. Space on the truck. Paper products take up more space and the stores had every category of product wiped out, so they never got enough TP to fully restock the shelf.
Once the scarcity hit, everybody realized they couldn't just nip off to the store for more of anything as needed., so when anything they might need hit the shelf, they grabbed it. If TP happens to be on the shelf when I'm in the store this week, I'm grabbing my two packs because I don't know when I'll see more. I would not keep doing that if I have at least one sealed pack left. But it's random chance when the truck arrives and the shelf has product and I haven't seen it in the store since before the hoarders hit three weeks ago.