i'd actually be happy to volunteer some time helping out if the people at 2+2 ever wanted to try making the forum stickier and easier to use
not in the engineering side but laying out the structure and stuff
i do this for a living and OP is right, there are a lot of things that could be done to better welcome in newer users, make posting easier, conversations easier to follow etc
problem is i'm 99.9% sure they are using off the shelf software and this would likely be more work than just a few fixes as a result
but yeah, you don't need to look at the numbers to know user growth has flatlined given most people posting these days have been doing it for a decade by now
we're probably losing more users to death and retirement than we gain each year