P.S. In my state in the US, and I believe this is true for most of the country, “commercial drivers licenses“ are required for driving very large and heavy vehicles over a certain weight; they are not required for driving paying passengers in a regular sized vehicle - in case anyone is wondering. You don’t need a special license to transport passengers for hire in typical sized cars, because the expectation is that you already know how to drive those vehicles safely.
A catastrophic vehicle failure at highway speeds could cause death but these kinds of failures are not especially likely, and drivers are expected to be able to reasonably handle circumstances they may encounter. The most dangerous circumstance I can think of off the top of my head that is not whether related would be the explosive decompression of a tire at highway speed, leading to loss of control of the vehicle. While the car might begin to swerve, a driver should react to this and keep the vehicle under control while they navigate to the shoulder. Catastrophic failure of brakes isn’t a common occurrence, and brakes begin to squeak when they are wearing down; the entire brake system would have to fail.
Interestingly, the FAA does make this distinction for pilots licenses: if you are going to fly someone in an aircraft for hire, then a private pilots license (PPL) is not sufficient, and you need a commercial license - even if you’re operating the same aircraft. You can split the costs of travel with someone if you’re both flying to the same destination, but you cannot fly someone else for hire and charge them for everything (in other words, operate a small airline or a charter service).
I can think of a number of good reasons for this: among other things, most adults with driver licenses quickly develop hundreds or thousands of hours behind the wheel of a car, and if the car malfunctions you can simply stop (most of the time — driving in extreme weather conditions being an exception to this). Private pilots engaged in general aviation may take years to reach 1000 hours flying an aircraft, whereas a professional pilot probably flies 1000 hours each year; and has a rigorously routine re-training and certification schedule (from what I understand) because an aircraft malfunction in the air is a very serious situation. Plus the amount of information that pilots need to know in order to fly safely is substantially greater than what drivers need to know; the maneuvers that pilots need to execute are much more cognitively and mechanically intensive, and the concurrent task workload is much higher.
A private pilot engaged in general aviation is the one taking on the risk of an accident, along with anyone they bring along (e.g. friends/family). When a (non-pilot) passenger pays someone else to fly them, they have little understanding of the risks involved in the activity - whereas most adults know how to drive or could easily get a license; and even if they don’t, they understand the risks of road travel - whereas non-pilots have few understanding of the risks of air travel.