I suspect, but don't know for sure, that this is related to funding for staffing in command centers and such. "Fly it until it breaks" means that somebody must approve an uncertain and ongoing expense without any results to show for it.
If you re-frame it as an initial experimental mission, it's a smaller and more defined budgetary request. You can outline potential extra-time scenarios, but presumably those are a lot easier to get approval for after the initial window is a success.
edit: It also occurs to me that framing it as a series of smaller phases with well-defined goals and benefits also makes it easier to communicate a straightforward message to the broader public about the mission.
If you re-frame it as an initial experimental mission, it's a smaller and more defined budgetary request. You can outline potential extra-time scenarios, but presumably those are a lot easier to get approval for after the initial window is a success.
edit: It also occurs to me that framing it as a series of smaller phases with well-defined goals and benefits also makes it easier to communicate a straightforward message to the broader public about the mission.