In short, no consequences. An inactive forum is likely a forum that is no longer looked after by its staff and therefore it is free publicity, especially if it had a very good pagerank.
CM30 said:
Because spammers are awful people, period. And because spambot software tries to post as much as it can before it gets banned (hence if no one is there to ban it, it'll go forever).
As much as I absolutely HATE spambots, and I am in disbelief over what I am about to say, I am not sure if I would go so far as to say that they are bad people. The people behind the posts are just trying to make a living and probably hate spamming someone else's forum as much as you hate to clean it up.
For all we know, they were some recently laid off worker who dedicated most of their life to a company that repaid their loyalty with a pink slip. And after weeks and months of no success on the job search, and burning through their savings on bills and other expenses, they reluctantly answered one of those "work from home" ads that you see everywhere, and had to swallow their pride because they have a family that they need to take care of and can't afford to maintain their indignant, yet justified attitude toward spam.
But the blame should go to the companies who pay email providers for your personal info and the keywords found in your emails and of course, the fat cats sitting in their fancy suits not caring about the people who voted for them or the economy they promised to do something about.