It only makes sense from an accounting viewpoint. The BBC did the same thing years ago, and sold off all their equipment, studios, staff etc to newly created internal companies. They then charge each other for services and the money just keeps moving round in circles within the overall corperation. That way the books look like
you are making a profit, and keeps shareholders / fat cat bosses happy... even though in reality you are loosing more money than you did before when you were one big happy family. It's the same logic as making your staff redundant then re-hiring them as freelancers at a higher rate.
It's no surprise that Chessington no longer use Studios, and get external companies to do all their theming work.