Our friends at W3C (World Wide Web Consortium), the body which looks after web standards, was once squarely behind the XHTML 2.0 standard. They wanted the web to be strictly standardized. However, browser vendors observed was that very few web developers actually developing XHTML to the correct standard, if they were even doing it all! So, the standard realistically had no relevance. Thus, a real-world evolution of HTML was called for.
One which would ensure that current web developement realities were accommodated. For example, many coders forget a tag, and that is forgiven by a browser. So, all these things had to be taken care of as an evolution of HTML. That’s why Opera, Mozilla and Apple came together to form a group called the WHATWG (WHAT working group) and they came up with a standard called Web Application 1.0, which was the defining moment of HTML5. The developer community was behind HTML5 instead of XHTML 2.0. The W3C saw the writing on the wall and then stated they would discontinue their work on XHTML 2.0 and will adopt HTML5 as new version of HTML. This is how the W3C adopted HTML5, which they originally opposed. Basically, they saw it was popular with developers, so they adopted it as the next step in HTML’s evolution.
A clear example of Darwinian theory in action.