Because by letting them know they could be stuck with their yes vote with nothing to show gets them to consider, 'is it worth in'. IOW, Do you feel lucky sucker..? It might just get them to reconsider.
Yes, but I would have rather they got blindsided by the fact, provided the entire bill died. If the Senate bill would still pass then I the strategy makes more sense to me. This whole process is a little convoluted to me. The only thing I know is that, if this passes, the days of filibustering are passed. If you are in the minority party you may as well stay home.