In an article on Friday, CNBC's Larry Kudlow perfectly explains why Ryan couldn't agree to such a deal:
The purest path for the budget talks would have been a clean bill keeping all the sequestration budget cuts. But the votes were never there in the House. Defense hawks and others would have left that bill short by 40 to 50 Republican votes. And Democrats would never have supported it. Hence the shutdown threat.
Ryan knew all this. So he went to work with Sen. Patty Murray on a common-ground compromise that pleased no one fully but at least temporarily got the job done and took the shutdown off the table.
Conservatives refuse to admit this underlying reality. What would they rather Ryan have done? Put forward a budget with sequester level spending? What happens after it fails in the House because Republican defense hawks vote against it?
These are the political realities that conservatives must confront. Instead of looking at the agreement and comparing it to their ideal deal, they need to compare it to the realistic alternatives. In this case, demanding a budget at sequester spending levels would have risked another government shutdown, distracted from Obamacare and given Democrats more leverage in the negotiations. Is that really what conservatives want?