I really don't mind twenty-page docs when they are well-structured, have a clear drill-down from less details to more details through the relevant parts, documents where I feel are guiding my reading towards the important bits I need at the time, and making me comfortable to get into the weeds when I feel prepared enough by understanding what's the general point of the document. It's actually pleasant to read those.
The issue is: almost nobody has (or puts in) the time to properly edit a twenty+ pages document to make it pleasant to read, I've been guilty of that too in the past and do understand it usually comes from having so much of the context in one's own head that it gets lost taking the view of someone reading all the context for the first time.
I've strived to be better at it for years and it isn't an easy skill to learn but in a larger organisation it's immensely valuable to save everyone else's time.