The main reason is that these are modern rides of the type that are still common in other amusement parks. The Mary Rose and Enterprise from Dreamland still operate at Henk Bembom's Loudoun Castle Theme Park. The Looping Star still operates overseas (and a similar model operates at Loudoun Castle), and I believe the Big Wheel does too.
We want Dreamland to offer something that can't be found elsewhere. We are trying to create a unique attraction which recreates the Dreamland of the mid-Twentieth Century with attractions that you would have seen at the main seaside amusement parks during that period. This is from the days when seaside parks offered big, bespoke rides.
As an aside, I would recommend a visit to Loudoun Castle. It has many of the rides that were at Dreamland in the 1980s and 1990s, including the Mary Rose, Enterprise, the second Looping Star, Wild Mouse, Pirate Ship, Apollo 14 and Regatta. Even the Stowaway ride from inside the Dreamland Cinema building in the late 1990s now operates at the park. The park comes highly recommended and its setting is truly stunning.
http://www.loudouncastle-online.co.uk/