I've got several theories on the matter.
One is that Republican leaders want the situation to appear hopeless, then ride in like white knights to save the day. "Whew, I thought it was an impossible task but we managed to somehow achieve the impossible." Applause follows.
Another is the Tony Soprano theory. Being a Washington lawmaker is a license to print money which largely ends up in your own pocket. The Republicans plan to milk the system as long as they can before they are booted from office or Civil War breaks out. Either is fine with them.
Neither theory is entirely mine, obviously, and if I had to place a bet I'd go with Theory #2.