69 is not radically different to 62 but 72 is. That means there needs to be a replacement at some point in the next 3 years, they need to come from the current crop of MPs, and they probably need some time in post before fighting an election.
That’s the actual context for the leadership discussion, not Corbyn vs Cooper, but at a basic level it suits everyone to have the latter because the actual leadership problem doesn’t have a solution. Unplanned as it was, the Corbyn project isn’t cohesive enough to have legacy planning and the biggest names in the shadow cabinet are political allies not true supporters. There is no easy continuation for Corbynism regardless of what Progress and Co do.
This is the best case scenario as far as I’m concerned. The worst case is the full blown split. I know I’m too risk averse for the current political landscape so I fully accept I might be wrong, but surviving a change of leader ought to be more politically practical than splitting the party. Except at the moment we seem incapable of avoiding the latter and the former is coming anyway,