Simply put, it's designed to make PDF output and provides a lot of quality-of-life tooling around that. Better support for CSS paged media and non-HTML XML inpu

Simply put, it's designed to make PDF output and provides a lot of quality-of-life tooling around that. Better support for CSS paged media and non-HTML XML input, better handling of page-spanning tables, shims for things missing from paged media (like hyphenation and ligature controls, PDF-specific objects to modify output with Javascript, Javascript embeds into PDF output), better out-of-the-box styles, better documentation and support, and more predictable output and better debugging tools. Browsers are catching up on paged media options, but they're not all the way there yet. The rest of the stuff Prince does is not (and arguably shouldn't be) in the scope of headless Chrome. There was a brief moment where headless Chrome supported flexbox in print before Prince did, but that was fixed a month or so ago in Prince dev and should land in production soon if it hasn't already.