Basically Html was created for text structure in documents and it is not sensitive because it need to be compatible with browser so has other markup language instead of programming you code and it is display there right on the browser...
The answer to this question can be so simple. Html is not case sensitive because its not a programming language. Just like CSS.
Mind you, all programming languages are sensitive most especially languages like C and languages largely based on it.
The HTML needs to be most compatible as possible, to be read on any browse. So, as like the HTML is not a programming language and just a markup language, threre's no need to have variables and functions, wich mean you can't create dynamic context, possibiliting to take advantage over "no problem with caps variables and functions names".
Following this logic, there are more flexibility on the way that HTML works, allied to necessity to be most readable as possible, same on the caps variation.
yes html is not sensitive markup language as xml and xml have container tag only but html doesnt have both container and empty tag like <br>, so you cant compare as html is an errorless language because web browser doesnt made like xml parser.unlike xml give error on little mistake
It's not a sensitive case, because the first browsers created their own standards and when HTML finally organized and regularized, the new browsers had to make a smooth transition in the code that was not so painful, the browser now strives to show what you type.