I still don't get it, HTML5 lets you write your documents in XHTMLish way. The spec doesn't care, you just decide. And tools should still work as expected
And BWT it was xhtml to broke backward compatibility "XHTML is not compatible with the IE8 and other older versions of the browsers. HTML5 is capable of using XHTML style tags but not vice versa. While writing code in XHTML, there are several restrictions that the developers need to adhere to"
HTML5 documents are not XML; this means that tooling that isn't a browser, or isn't 'HTML aware' became excluded. The web 'special cased' itself at this point, and HTML and common data processing pipelines of the time parted ways, this is my only point.