The author is left unnamed (actually the authorship is signed as 'collective work by SoftPress team).
I can only guess that the engines in IE5/Netscape3/4 were so slow it really was the only practical usage of the language.
Today it took me only 5 minutes to convert a slider application from jQuery to Mootools. Complete with animation and all. It is working in Firefox 3, 3.5, 3.6, 4, Chrome 7-12, Internet Explorer 7,8 and 9. I wonder, how much time will it take to write the same thing, working across browsers, 10 years ago?