For fiscal year 2011, the House Republican leadership brought to a vote, and the House passed, 4 bills (that eventually became law) that funded the government: Continuing resolutions on 3/1/11, 3/15/11, and 4/9/11; and a budget for the remainder of the year on 4/14. None of these called for the repeal, defunding, or delay of the Affordable Care Act.
For fiscal year 2012, there were 7 bills: Continuing resolutions on 9/29/11, 10/4/11, 11/17/11 (this funded some departments through the remainder of the year), and 2 on 12/16/11; disaster relief funding, also on 12/16/11, and a final budget on 12/16/11 as well.
For 2013, there were 4 bills: a CR on 9/13/12, disaster relief supplementals on 1/4/13 and 1/15/13, and a budget on 3/21/13.
In none of these cases was there a serious threat of shutdown if there wasn't some rollback to Obamacare. Of course, the Republicans managed to extort the sequester, and they've voted to repeal the ACA separately 40+ times. But not until the last few weeks were they actually holding the government or debt ceiling hostage with Obamacare as the ransom demand.
So why now? Why not in 2011, when they could at least claim some political capital? They had just made historic gains in Congress, running in 2010 largely on a platform of repealing* Obamacare. So why wait until after they were repudiated in the 2012 election, until states had spent millions on implementation, and now, thousands of people had already signed up?
Maybe it's the gradual collapse of their alternate-reality bubble: In 2012, they thought the Supreme Court would overturn the ACA, so they could satisfy themselves with show votes for repeal. Then in 2012, they thought they were a lock to take the Senate and the White House. But there's still that pesky budget bill in March this year. Could it be that only now, at the 13th hour, are they facing the fact that Obamacare isn't magically going to go away because they wish it so?
I don't have good answers to these questions. But they're worth asking, because I don't think the Republicans do either.
*and replacing, but don't worry your pretty little head about that.