My generous take, Rolex doesn't get much respect for their movement aesthetics and they want to demonstrate that they do put effort into this area.
I lean more towards my cynical take because we also saw Tudor use exhibition case-backs on their 18K gold Black Bay 58 and the Black Bay 950 and those movements are not very nice looking. It would be hard to convince me that was not done as a cost-cutting measure. Rolex are not Tudor, but I can't help but notice Rolex only includes exhibition case-backs on precious metal models currently.