The Atlanticreports that since many businesses and manufactures didn't expect the pandemic to last for over six months, there are supply issues in "all sorts of categories: food, cleaning products, medication, exercise equipment, outdoor gear, furniture and home decor, renovation supplies, home electronics, office supplies and lounge wear."
Those shortages stem from China shutting down earlier this year, which led to assembly lines in countries such as Vietnam and South Korea going idle. And while China has started manufacturing many goods again, the shipping industry has a labor crisis because for many workers their home countries’ pandemic travel restrictions prevent them from coming ashore. And that means less cargo ships to bring items to the U.S.
One more key cause -- the fact that retailers use the “just in time” inventory model. They keep their costs low by keeping very little on hand, and shelves are restocked with freshly delivered products -- which haven't been arriving.