I am not seeing it used much in print though.

That’s because print is an additive medium and requires support for additive colorspaces (CMYK) and device color profiles.

This is probably coming to CSS in the coming years. [0] Which makes me very excited for one reason: CSS is nearing feature parity (and surpassing it in some areas) with Adobe InDesign, so we can finally ditch adobe and just make print publications within the browser. The only other thing missing after custom colour profiles is a proper text justification algorithm, although, for many, it's not so important because people are already used to reading ragged text.

[0]: https://www.w3.org/TR/css-color-4/#color-space

It's in the CSS Color 5 spec - here: https://drafts.csswg.org/css-color-5/#cal-cmyk

I don't understand how this is still a thing in 2024.

It’s essential complexity, so it’s not going anywhere.

I would maybe say that it is almost assuredly one of the most featureful and widely used layout technology. But I'm not convinced it's the most powerful, flexible, or even advanced. It suffers from significant performance issues due to legacy baggage and a poor underlying abstractions. There is a reason anyone building things like visual editors, spreadsheets, et al tend to drop into lower level rendering technologies.