East Asians and Central Americans flock to all sorts of low-paying jobs, but you hardly ever see them driving taxis or trucks (long-distance, anyway).
The stereotypical cab driver is from north and eastern Africa, the Middle East, and the more northern and western parts of South Asia. Occasionally from Western Africa. The stereotypical truck driver is a restless Scotch-Irish hillbilly.
Being adapted to a more nomadic way of life certainly helps if you're going to be driving around all day. That weeds out the East Asians and some Mexicans, who are designed for sedentary life in large-scale intensive agricultural societies.
That still wouldn't weed out most sub-Saharan Africans and other Central Americans, whose horticulturalist ways also involve a good deal of moving about. They certainly enjoy going out cruising, but they wouldn't want to transport others for pay. They're too wary of strangers.
A cab ride is only a little different from hitch-hiking, so trust is crucial. Low trust will make the cabbie think that the customers are going to kill him, rob him, or skip out without paying. Low trust will also keep customers from getting in, thinking that they're just going to get ripped off.
It's a kind of guest-host relationship, where the taxi driver is the merciful host willing to help out the stranded guest, expecting a little something in return. Cultures of hospitality are the same as cultures of honor, since they're just two forms of an obsession with reciprocity. Hospitality is kindness repaying kindness, starting out generous; and honor is harm repaying harm, starting out threatening. And those both are found almost entirely in pastoralist societies.
The most helpful taxi driver I've known was from some herding region in East Africa. He was wiry, had a thinner and more pronounced nose than other black-skinned Africans, and spoke with pharyngeal consonants, unique to the Afroasiatic family that includes Semitic, and is mostly spoken by pastoralist groups. (It wasn't Arabic. Maybe Amharic.)
I wanted to make sure he got a tip, but the meter was running a little close to what I had on me, so I asked to be let out a couple blocks before the spot that I'd first said. He immediately sensed why I'd changed my mind, and said he'd turn off the meter and take me home, that I could pay with whatever I had -- "It's too cold for you to walk tonight." After I apologized that the tip wouldn't be that much for a late night trip, he brushed it off saying, "Oh no, that's too much anyway."
He may have been an extreme case, but you can't hold down a job like that if you don't have at least a milder level of that generosity. There will be too many complaints about how rude and inhospitable you are, and you'll get fired. Most times you may not even know that the person is generous because they won't be put to any test. You'll only find out when you're a little short. They're really one of the few groups of workers who are willing to cut you a break when you're in a bind.
Now, driving trucks long-distance doesn't tap into the guest-host psychology, but it does require drivers who can deal with and even enjoy long stretches of solitary, adventuresome activity. That's perfect for someone built to follow a herd of livestock, which isn't a big-group affair.
It's not hermetic either, though: bouts of close socializing punctuate the on-your-own flow of time. For herders, it's reuniting with kin, boisterous communal festivals, and the all-important guest-host relationships like stopping at a caravanserai to mingle and rest. For truck drivers, it may have been a honky tonk bar or a rest stop with a greasy spoon diner, places where you can interact face-to-face and even get worked up into a crowd-vibe with people trusting one another enough to cut loose and have some rowdy fun.
I wish we'd grown up living closer to my father's father, who was a truck driver. We got a good deal of exposure to footloose, unpretentious living through my mom's side (Appalachian hillbillies), but it would've been better if we'd gotten more from my dad's side too.