According to the article Cloudfront is paying, but is paying "a fraction of what reCAPTCHA would have [cost]". Recaptcha is $1/1000 challenges, so apparently hcaptcha is some small fraction of that.
Cloudfront might get a discount for running some of the infrastructure on their own servers, on the other hand that might also be an integration hassle that actually costs them money.
This seems unwise, because many captcha farms charge less than this. A quick Google search shows one service offering $0.50/1000 challenges. If it's 2x cheaper for an attacker to solve a captcha than it is for a provider to display it, it sounds like the attackers win.
True, the attacker is much less likely to have anywhere near the funds of the target, and they don't want to hurt them.
Regardless of the actual price multiple, it costing anywhere near the price to serve as the price to solve just seems to defeat the point. Really, it costing any money per captcha served just punishes sites that happen to face a higher volume of bots, even if they're a small site. It's just going to push the company to switch to a different captcha service, which may be even cheaper for attackers to solve.
[1]: https://www.hcaptcha.com/#plans