The reason is simple, HTML is not a hypertext markup language. Markup is the process of adding commentary and other information on top of an existing document, and HTML is ironically incapable of doing the one thing it most definitely should be able to do.

It's so bad, that if you want to discuss the markup hypertext (I.E. putting notes on top of an existing read only text files, etc.) you'll have to Google the word "annotation" to even start to get close.

Along with C macros, Case Sensitivity, Null terminated strings, unauthenticated email, ambient authority operating systems, HTML is one of the major mistakes of computing.

We should have had the Memex at least a decade ago, and we've got this crap instead. 8(