The reason is that it costs money to maintain the community area, we have power, wifi, water line maintenance and other costs such as house repairs, weed whacking, etc. and in order for the owners to not have to spend too much money the community areas charge money to use the facilities, to stay as a guest and rent a room, for other items that are sold as well as services (quad or motorbike trips or workers that we have to pay)
Hope that helps understand the costs involved and why we have to charge you.