Ted Cruz is trying to defund PP. In order to get all of the GOP senate and at least 7 RATs to vote to defund, he is being coy about who is 'shutting down the Government' and over what issue. It is preferable to achieve a successful cloture vote if it is the minority that is 'shutting down the government' rather than the majority.
I'm sure Ted Cruz would prefer to have the luxury of just saying ... "I ... would shut it down."
You have the luxury of maybe one or two of these kinds of "position forcing" votes every 10 years, and if you can't be sure that it will absolutely paint the two sides as they need to be painted, it's usually counterproductive.