MARQUEE started out as a "feature" of very early versions of Internet Explorer, as a way for IE to differentiate itself from Netscape. (Don't hate Microsoft too much for this -- they were just following the lead of Netscape, who had their own proprietary tags. Heck, IMG started out as a Netscape-only tag.)

There was a real danger for a few years in the mid-'90s that competition between browsers would manifest itself in a proliferation of proprietary tags that only worked with one browser or another. The old "Best viewed with..." buttons that sites used to festoon themselves with (examples: http://cjihrig.com/blog/wp-content/uploads/2011/12/best_view...) were an artifact of this; they advertised that a site used one browser or another's particular set of proprietary tags, which was how you positioned yourself as "cutting edge" in, say, 1996.

Things are better now, thankfully. (Not much better, but better.)