Why HTML being used to create webpages?

HTML (Hyper Text Mark-up Language), is used to create web pages as I do every day. It is used to display images and text in the right way to create a web page, this is used alongside CSS (Cascading Style Sheets) to make them look nice, http://www.flowwebdesign.co.uk/, this site has barely any html, to see this right click and click view source, but has about 150 lines of CSS, combined you can make some great looking web pages.