That’s part of it. There has been a driver shortage for the past 5+ years. And as such, there’s little to no capacity available in the system for a sudden surge in demand. There’s a brief surge in freight volume in spring and before the holidays, and most carriers are scaled to handle that as their maximum. No extra equipment or drivers to handle anything beyond that. There’s also the change in the way retailers are ordering product that is a factor. Everyone wants to run lean, and relies on “just in time” logistics to replenish their inventory. They don’t keep massive warehouses loaded with huge stockpiles of inventory anymore. They order enough for the week, and that’s it. The less inventory you keep sitting in the warehouse or on the shelf, the lower your overhead, and the better you look to your investors. A steady stream of small shipments instead of huge ones. Which works fine for 95% of the time, but when something interrupts that flow, such as stupid panic buying wiping the shelves of a months worth of inventory in an hour, or a carrier shutting down or going on strike, is when you see the shit hit the fan. The carriers can’t keep up with the hugely increased demand even if the manufacturers were able to pump out the product fast enough to keep up with the retailers ordering.
tldr
Penny pinching to please investors leads to retarded just in time logistics being the norm, and when something not normal happens everything goes to shit