And those "pretty docs" are what attract people to make content for Forge in the first place. I can't write anything to the github pages myself because obviously I'm not sure what to put down. I like to think I know how to write technical documents, but I also need to know what the hell I'm talking about. I (or someone) need to sit down with at least one dev and go through at least some basics with them. Like, for example, what does Forge always expect a mod to have? What file structure does Forge expect? What are some examples of very simple mods, and how would they all work under the hood basically? Although, of course, you should be able to understand what a function does by looking at it, it doesn't answer other more pressing questions about the Forge API as a whole.
Hell, if I just had a week with a dev where we just devoted a few hours to hammering out the documentation, then I'm sure we could make a huge dent, if not entirely complete it. I absolutely get that Forge is a big project and it needs a lot of time, but if these documentation needs aren't met, then many people are just gonna get frustrated and go work on something else. And you don't want that. You obviously want more people to use your API.
I also get that documentation isn't exactly a glamorous job. It's a very underappreciated part of making an API. But I think it will absolutely pay off in the end. It would address a lot of threads that are constantly getting made in the Modding Support sub-forum asking things that good documentation could easily answer. It saves your users time and it saves you time as well. Everyone's happy.