When car manufacturers open up after Covid shutdown, they started seeing massive demands. We couldn't keep up with their demands since July. They learned their lesson from Covid and not taking any chances this year.
For what it's worth, my somewhat educated guess from someone who covers Autos slightly:
2019 was expected to be a "peak" year in the automotive cycle, so everyone in the supply chain adjusted accordingly by modeling in lower demand following that peak. I'd wager with COVID-19 the trough came significantly faster (and deeper) than anticipated, and as we gear up for an equally fast (expected) recovery, inventory levels aren't adequate.
Are there still shortages in some places? In my (EU) country at some points the shelves were half full, but there was never anything out of stock. I'm somewhat surprised they didn't sell to other countries, we can drive a truck of tomatoes across Europe without problems, why not toilet paper?
Where I live in the US, the shortage only lasted a couple weeks, where you couldn't get certain brands. There was only a few days where the shelves were totally empty. I work at a grocery store so I saw the whole thing start to finish.