McConnell's overall strategy has been to try to have the most Republicans in the Senate as possible so that he'll have the best chance to pass conservative legislation. As part of that,
he doesn't hold votes that he knows he'll lose and that may harm some of his Senators politically. McConnell takes the resultant heat from conservatives, who really want to see the RINO's put on the record so they can (so the theory goes) be put on the record and then replaced by someone more conservative.
In any case, I think that to him, this is the "payoff" for all the heat he takes. In his mind, this vote succeeded because he knows when he can push, and when he can't.