About a year ago, SU made the decision to start double mounting some of their larger stamp sets. They felt this would be a good way to get stamp sets with several pieces into a lower price range--since double mounting would reduce the number of wood blocks needed for the set.
This has not, however, been a popular decision for demonstrators and customers. Therefore, SU is determined to look for other ways to reduce their costs and bring the price of these types of sets down. This means that with the exception of some stamp sets, they will no longer be creating double-mounted stamp sets.