The only text that appears (and prints) in Outline view is text that's in Title or Body Text placeholders (the things that say "Click here to ..." on newly created slides).
Often, people resent MS telling them what to click or where to put text and just delete these, or start with slides based on a blank layout, one that has no Title/Body placeholders. No text in these placeholders --> no text in the Outline view --> nothing to print as an outline.
For this and other reasons, it's generally best to work with PowerPoint rather than against it. Generally. There are always exceptions to this rule, of course.