Because he kept delaying the vote to go nuclear. Next week.... next week.... next week for sure.... Finally, on the eve of the vote (for sure!) this "deal" was struck. Maybe you think it was just a coincidence? Not me. Not in a million years.
But it doesn't matter now, because Frist still has his finger hovering over the button and he WILL have the votes when he is finally forced to push it. And now, there is no way the rats can look good when that day comes. (And it will come.) The compassionate, majority Republicans "compromised" - - they TRIED, they really TRIED, to be nice to the minority Democrats. But the Democrats showed their gratitutde by up and stabbing the nice Republicans right in the back....
If you are correct that Frist did not have the votes, that makes the deal a *little* sweeter.
But it seems most observers felt he did have the votes.