We cannot read their minds, but it is likely because of the success of their respective first versions. Both these mattresses have been well received in the market, and in the GhostBed vs. Purple mattress battle it would have become evident to GhostBed that its cooling properties needed improvement, and to Purple that they needed a range of comfort levels, not just the one. Most developments are based on consumer comments and demand, while a few are also carried out in response to the progress of modern technology (e.g. phase change technology).