It's a difficult one. I'm fuming about the way doubles players seem to be cast more and more like second class citizens, almost to the point of extinction if some people had their way, given the bollocks ideas being put forward recently for "progressing" the doubles game 
And yes, it's not right that singles players withdraw from doubles, at any stage of a tournament, at the drop of a hat because they (quite understandable at times) want/need to concentrate on singles. Especially if they took a place in the draw from a doubles specialist.
But Jack has said that he wanted to play doubles to (hopefully) improve his net game, which is a perfectly valid reason.