Content matters for row height, as does fonts, styling, etc. Footers, too. The number of footnotes (thus the height of the footer) can depend on the page content, too.

Maybe there's an image in there, or some sort of specially styled content that makes the line height larger than normal.

You have to be able to render the row to know the final dimensions, to be able to make a call whether it should go on that page or the next. If you don't, then you end up with one page actually rendering over into a second page.