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I think is is based upon the fact that the Selectors have no faith in other openers currently playing in County cricket,
and,
the Ed Smith plan of selecting the best (fit) players and leaving Bayliss, Root & Buttler to find a batting order. (Smith denies any input into Moeen at 3). Ben Stokes does seem to have found a slower gear, presumably to show he has a sense of responsibility after his Bristol escapade.
Well all three must have been on the pimm's because you'd have to be half cut to think YJB has the technique or temperament to open the batting.
edit - but it shows the dearth of talent we've got that these are solutions people are serious about.