Now that the Democrats know the Republicans are planning to defect after the first vote, why on Earth would they compromise? Moreover, what is the point of taking the hit by filibustering reform in the first place? It could work, in theory, if you could bluff the Democrats into thinking the GOP might hold the line indefinitely. But I'm pretty sure the Democratic party has access to articles published in Politico, which means the jig is up. So now the Republicans are trying to bluff in poker when they and their opponent know they have the weaker hand, and their opponent has heard them admit that their strategy is to bet for a couple rounds and fold before the end. Why not just cut their losses now? This makes zero sense.
Doesn't seem to make much sense, does it? My guess: the GOP leadership is trying to make a show to Wall Street that they're willing to take a hit in order to do their bidding, so that the banks will give more money to Republicans this year. If the new regs pass (and I think they have a damn good chance of passing), then it's something of a win-win for both parties if you consider the money angle: Republicans showed they will stand up for Wall Street, Democrats showed that they stood up to Wall Street, the former gets money and the latter presumably gets more of a clean slate when it comes to voter anger about bankers. The assumption here is that the money will help Republicans in November more than the charge of standing up for the bankers, which might well be true if the bill actually passes and voters move on to other issues. But it smacks more of trying to make the best of a losing hand with respect to the policy.
This is all very cynical, but it is Mitch McConnell we're dealing with here.