Not sure you can conclude that most can’t afford the ad free version from what’s publicly known.

They still sell both versions, presumably if only very very few people bought the ad free version then they would have stopped selling it.

Just had to replace a Kindle. They sell one version now, with ads, and you can turn them off permanently by making a one-time payment though your Amazon account. They also offer it as a check box during checkout.

I bought a Kindle a few years ago. At the time I wasn't working regularly so didn't have much cash. As a result I didn't check the box and have ads on my Kindle.

The ads are almost entirely irrelevant but seem benign enough since they're always for other books (mostly self-published, I suspect) in the Kindle store. They're also limited to the lock screen so hardly intrusive.

It's only recently that I've occasionally considered paying the £10 (?) to get rid of them and the reason is pure vanity: I'm now (fortunate to be) in a fancy job with a fancy title and I don't want to look like a cheapskate.