[pier25]

For 4 years I worked at a publishing/education company and developped on a solution for educational interactive ebooks in HTML.

A couple of insights from those years:

PDF is popular because it fits the paper designer mindset and because Adobe InDesign is pretty much the standard in the publishing industry.

HTML is a much better format for the digital age. It's responsive, interactive, etc, but even today, the best way to produce HTML is by using a code editor.

Even if there was a good WYSIWYG tool, editorial designers come from the paper world and have a really hard time understanding the responsive model.

Many times I've fantasized about working on a tool made for designers to produce HTML, but it would be a ton of work and I don't really think there is a market for it. Many ebook formats are actually HTML, but I think the industry is getting by with conversion tools from Word. Most HTML content comes from blogs and journals which already have an established pipeline and don't need a general purpose HTML production solution. Education is the strongest use case, but most education companies are still rooted in paper and switching to interactive education is quite a leap.