Why did Turnbull let this get this far?

How could Malcolm Turnbull have let this idiotic idea develop into a test of leadership?:

Kevin Rudd’s two-year bid for the post of UN secretary-general is expected to fail today because of strong cabinet opposition to the Turnbull government nominating the former Labor prime minister for the job.

Foreign Minister Julie Bishop is expected to raise Mr Rudd’s request for Australian endorsement for his campaign for the top UN post at the cabinet’s first full...