you've obviously never run a forum before. I have some access for AVA axis and allies forums. each person has to be given rights, its not on a "password the door" type bases.
its a ton of work if you are forever moving people from one forum to another. people have to be removed and added constantly because of the side switching going on.
as an example, JG54 switched this month for allies instead of axis. there are 12 consistent members that would need to be taken out of one forum and added to another.
no lets take a larger squad like claimjumpers or JG11 in its heyday. whole different ball of wax.
the other problem you run into is if someone is forgotten? now you have to deal with issues like "cheating" or "spying". yeah not much fun.
im pretty sure email is the better solution and so far has worked ok. while I wouldn't mind such forums, I know how much of a nightmare, logistically, they can be.
and lets not forget, no one is getting paid to do this. this is stuff that's done on our own time.