But driving instructors make so much money that they can afford it.
That is so far from the truth.
Like any self-employed person, there are a limited number of hours in any day, so that limits the number of hours workable. That caps the available income.
Throughout my time as an instructor, I've had so many sales calls from organisations pronising to help increase/expand my business. Only way to do that is to work more hours, or charge more per hour. The latter just reduces income, if uncompetitive.
When I started, 2004, I was teaching 4 2-hour sessions per day, 5 days a week. At £19/hr. £760/wk, £38k/yr (2 weeks off) Sounds wonderful, until you look at the franchise fee of £15k, and a fuel bill of around £5-6k.
But that many hours with learners can blow your mind. Few can do that continually.
I soon reduced my hours to 3 sessions a day, often only two, but of course the fuel reduces too.
Now I only do 2 days/week, and no learners. The fleet work pays flat rates per job, which equates to a lower hourly rate, but reduced fuel costs, as we use their car/van. But, can travel up to 50 miles, occasionally more. Whilst fuel is paid, wear & tear are not. But now with my own car, costs are much less.
There's a lot of juggling.