Why the name coined for MARKUP LANGUAGE for SBML?
SBML follows in the same vein as XML, in that it provides a standardized and flexible method for structuring information. XML and its ilk aren't just for making web pages, they're for sending structured datasets between systems and programs (in fact, XML is a fairly common configuration format). Why? Because the structure makes parsing simple (well, simple-ish).

BTW, markup languages were not invented for the web, HTML was far from the first one. The origin of markup languages is typesetting and in fact one of the most common uses these days is still in writing papers (ask a local math/physics/CS person what he/she uses to write papers and the answer will be Latex...a markup language).

Edit: BTW, this really has nothing to do with biology and you could have at least read the wikipedia page on what a markup language is.