I can code up a complex HTML table by hand faster than I create a basic MD table, but other than that, I find it difficult to achieve a good writing flow with pure HTML, even with all the automation. I author a lot of API docs, READMEs, and how-to guides, and find MD to provide the perfect mix of decently powerful markup and flexibility with supporting raw HTML when needed. The only constraint is that some markup renderers don’t support or severely restrict HTML passthrough (I ran into this with GitHub recently).