When I was getting my degree, we had a course about how to market yourself as a job seeker, and one thing our teacher had a strong opinion on was that your résumé should be no longer than two pages (I live in the US). I've seen this recommendation from many other places since then, such as hiring managers, human resource workers, career guidance counselors, etc.
Why is it recommended that your resume be only one or two pages in length?
I would prefer a comprehensive recommendation, along with some links to research backing up the reasons for this recommendation, if possible.