Uh, paying for DNS isn't uncommon? Examples off the top of my head:

- Akamai DNS

- AWS Route 53

- Azure DNS

- Cloudflare (excluding personal/hobbyist plan)

- Google Cloud DNS

And many, many others. And I note the site you posted this comment on is using Route 53, so probably paid as I doubt their query volume would be in the free tier.

Paying for DNS for personal/hobby stuff is probably pretty uncommon, because like you say, most domain registrars will offer it for free. But commercial websites often will, particularly larger ones with serious traffic.