Why do some documents/web pages scroll fast while others scroll slow?

Why do some documents/web pages scroll fast while others scroll slow?

This is normal behavior caused by the content itself. Each scroll step moves a fixed number of lines, but the text size and layout density vary across documents and pages — dense, small-text content may skip many visible lines per step, while large-text or spacious layouts move only a few. As a result, the same scroll action can feel faster or slower depending on what you're viewing.