Looks it's been known to be an issue for a while:

https://www.freightwaves.com/news/driver-shortage-ata-estima...

https://www.reutersevents.com/supplychain/3pl/12-key-facts-a...

https://www.fleetowner.com/operations/drivers/article/216917...

Even as early as 2005: http://www.iitr.edu/pdf/ATADriverShortageStudy05.pdf