Think of it in the context of why you send out a resume in the first place. Contrary to how it might seem, it is not to get you a job - nobody is going to read every word and get all excited about every detail and then bump you to the top of their list.

Instead, it is about getting you an interview. You want them to be able to skim the resume, see some good chunks of potential in it, and want to know more. That way, they will call you.

A long resume is going to have too much detail to make those highlights stand out. Your content will fight with itself to get the reader's attention. It is going to make someone sorting through a (sometimes literal) pile of resumes just think, "I don't have the energy for this" and throw your resume out.

Think of it for what it is - marketing. Get someone's attention, show them you can solve their problems, and make them think: "I should call this person."