It's a pretty standard/common assumption that employees that are paid more are willing to take on more responsibility and care more about their job.

> Maybe they need the job more because they can't just go make more money driving a big rig and are then less likely to jeopardize it by doing something wrong.

This hypothetical is unsubstantiated, and I can easily flip the script: How do you know the non-CDL drivers need the job more when they can easily just go work for Uber, or at a Taxi company or similar?

> Plus, the driver of a smaller vehicle has fewer kids to care about, so the same amount of caring goes less diluted. If you get into a collision, the driver only has to take care of 8 kids instead of 40.

Presumably, more caring drivers (even if they have less "care per kid") will get into fewer accidents, which will be a magnitude of impact more than any actions taken after an accident ever could.