Like how it is in many countries around the world, driving taxis is one of the easiest jobs one can get without much school education, as long as you can drive and communicate with customers. After working as a driver for 10 years, you would be qualified to become a freelance taxi driver which would allow you to do side businesses.
So, for someone who doesn't mind driving for hours (which usually means that they love driving and tending their cars) but cannot get or do not want to do other jobs for one reason or another, taxi-driving is one of the most typical jobs to "make an ok living" safely and legally.
To become a freelance taxi driver (kojin-taxi), you need to be 64 years old or younger. But back in the days, there was no retirement age. So, those who became freelance before the year 2002 can legally drive at any old age. For those who started later than that, the retirement age is 75. Meanwhile, some taxi companies may not have any retirement age.
A lot of drivers seem to prefer a straight far-distance ride as opposed to short-distance ride with a lot of turns. The former is more comfortable for the driver, and the money is better considering how easier the driving is. For this reason, some drivers only deal with their usual wealthy and long-distance customers. Back in the days, they would even ignore customers-to-be to avoid short distances.
Nowadays, they're not allowed to ignore customers, and since the economy hasn't been good even pre-pandemic, they often have to stick politely to the short-distance customers. (So, if I'm blessed with a nice driver when I'm riding a taxi just for luxury, I personally try to tip him/her by asking for no change.)
In the cities, there would be workers at taxi stops who would often call taxis so that there would always be enough of them to accommodate people getting off trains. There are also certain stations that attract long-distance customers, and taxi drivers think it's worth queueing at those stations.
But in rural areas where most residents drive than ride, or in residential areas where there are no trains to carry a large population, you typically need to phone for taxis unless you're fetching them at a big train station. As ITO implied, it's extremely difficult to fetch a taxi on the streets of Los Angeles while it's extremely easy to fetch one in Manhattan. Same thing in Japan.
Apart from what I hear from a driver friend of mine, drivers would often tell you these interesting stories while you're riding their taxi. I also love the NHK TV series in which each episode introduces various drivers at a certain city. There were a few episodes about cities in Japan.
https://www4.nhk.or.jp/P3607/