I’ve seen that too, but I still find out of date documentation much better than none. It gives you a good starting context and the code can complement the rest.
Though I guess I’m not really talking documentation of the kind open source projects have or commercial software provide. I mean design and architecture artifacts, which often do also include diagrams, and operational run books.
For business folks, that’s why I like putting a link to a wiki. In the wiki there can be subpages (or attached word docs and all that, which some were docs written for a business audience and others for a more tech savvy audience.
For diagramming I have the same problem as you, but I’ve been using draw.io for a while, and it’s the best I’ve found, even though I still don’t find it too great.
More recently (and with work from home), I’ve been considering getting this: https://www.wacom.com/en-us/products/pen-displays/wacom-one and just hand drawing all my diagrams.