VS LAS-MAN is only a three day a week flight, and ends within a month. In fact booking a revenue ticket is all but impossible except for certain dates after this.

LHR-ATL/NYC/BOS/DTW/MSP/PHL/SEA/SLC, Edinburgh-JFK, and MAN-ATL are the only routes UK-US/US-UK that can be booked as awards by VS. I'm guessing this is due to the agreement DL had to reach with JV partners AF/KLM/AZ in order to enter into a JV with VS. MAN-ATL is operated by VS, but I believe was included because DL was planning on operating the route using it's own metal at one point.

Since the VS LAS-MAN flight is ending, it means there is no options under the agreement that can be booked between LAS and UK.