This is a great UX addition. Why did it take them so long?
For example, HTML isn't divided into numbereres pages while PDFs are. A lot of latex interacts with page boundaries. Figures tend towards the tops of pages. And there's \clearpage. And the reference list might say which page each citation appeared on. All that stuff needs someone to decide how to handle it and then to implement that handling. Like... what value does \pageheight return? Sometimes I resize things to fit the page height, and if it was doubled then I should have resized to fit the width instead.