Honest answer to your question: Because they have to-do lists a million miles long, and "make an HTML-only version" is often at the very bottom of that list, be

Honest answer to your question: Because they have to-do lists a million miles long, and "make an HTML-only version" is often at the very bottom of that list, because it may require high investment while providing few benefits relative to other things on the to-do list. Also, because "giving users control" can mean a million different things… colors, fonts, sizes, dimensions, HTML vs JS, etc.