See: https://www.fmcsa.dot.gov/regulations/hours-service/summary-...
For long-haul it's probably a bit different, but other routes have a lot of annoying delays.
E.g. waiting at a port, waiting for a trailer replacement, waiting for receiving, etc.
Afaik, these are all classified as driving hours for logbook purposes.
It creates a situation where you legally have to park a truck on the side of the road when you hit your cap, even though 1/2 of your day might have been waiting around for something.
Imho, that's a bit ridiculous, and I'm sympathetic to shadow logbooks there.
For the 16 hours straight cross-country pounders, less-so. But long-haul is what autonomous trucking will likely eat first.
This is from a popular 90s country song:
sleep would be best
but i just can't afford to rest
have to be in Denver at morning light
- much too young to feel this damn old