It was just the style at the time. There weren't a lot of HTML editors, even in 2001, and those that existed typically defaulted to an entirely blank page. People mostly wrote web pages in something like an emacs, vim, or notepad. Dreamweaver and Frontpage existed back then, but DW was only really popular with professionals, and nobody ever really used FP.

This style was a popular choice because it was easy to write, and could be displayed by just about any web browser. Compatibility and low resource usage was important back then.