> Most website do not have a print CSS, so it doesn’t print that nicely in PDF.

Can't they just render the screen content in a pdf ? Seems easy for other programs to do this.

Viewport size and deciding where to paginate makes a naive approach to this surprisingly difficult. That being said, if you can control the css / html, you can often solve these problems with a short media query and some hints at where to break pages (e.g. https://developer.mozilla.org/en-US/docs/Web/CSS/break-after).