You’re assuming that the advertising on the forum pays for the actual forum, let alone the people who help run it too.
I know the advertising on here pays for the forum (or at least it certainly used to).
As others have said, it’s been done to death. As with sdb, I’m pretty sure I was buying the mag long before I found the forum.
I don’t personally subscribe as I’m now in oz and I hate emags. I was willing to explore international subscriptions to the paper version (and associated P), then Mark decided to have a petty argument with me over whether or not I was a customer, which sort of made up my mind on that one…