alt Hacker NewsHow would one do an if condition or enumerate a list in HTML alone? For that functionality you need another language to generate/manipulate the HTML.. not to mention interpreting HTML for display.
HTML is a markup language, it's even in the name... but it's not a complete programming language by any stretch.
It's not Turing-complete, and as you say, it's a markup language and it's not general purpose. But neither is a necessary component of "programming language".