It is said that pure outlining almost went extinct because of competition from word processors, but if memory serves, Word had an outliner very early on. Another problem for the competition theory is explaining why outliners are coming back into vogue, with three new outliners on the Mac and on Windows each.

Here's a different theory. Outlin benefit from the electronic outlining advantages of collapsing and folding text, hoisting headings, and rearranging by marking and gathering, and these advantages require on-screen editing. On-screen editing appealed to fewer users with the advent of color CRT screens and their less distinct text. The Mac in particular--the home of the first outlining boom--was initially committed to ultra-sharp black and white screens. When the Mac had to embrace color monitors, editing text on screen appealed to fewer users.

As large low-cost lcd monitors become available, on-screen editing becomes easier than ever before, giving outliners a bright future.