I'd disagree. Numerous studies with large sample sizes show the average sleep in America is 6 hours and change. I'd need to see some hard evidence that there are "a lot" of people, that is, a statistically significant number of high-earners, who sleep 8-9 hours.
In fact, there is evidence to the contrary of your claim:
>Turns out, the difference is pretty negligible — the "successful" people get 12 minutes less than the average American. According to this 2013 Gallup poll, the average American gets 6.8 hours of sleep every night.
https://www.npr.org/sections/thetwo-way/2015/12/24/460929475...
I track my sleep as best I can, and nearly-seven is sustainable, while a bit more than six on a consistent basis leaves me feeling pretty wrung out.
The extra 45 minutes we're talking about here are likely to be mostly REM, given how intensely I dream when I start napping to make up a deficit.
I think you may be having a selection bias here: there is a lot of people who sleep 8-9 hours at night who are in high income brackets (I think that’s what you mean by “successful”, even though that’s a debatable metric).
The healthcare problem is a US-specific one, although probably if you are in a union job you’re likely to be getting decent healthcare while working hours that let you sleep.