There is a difference, between forums that make money and that do not.
Also, the cost involved is not meek either. So if you are not good at investing money without returns and begging people to join your forum, the closing and opening thing is going to happen.
Plus, there is more than outsiders could see from running a forum without benefits. You get knowledge unlike any other. Get to know information that is exclusive to webmasters. Which you can use in many other ways.