When the cluster coordinator changes or a merge view is received, the new coordinator tries to reconcile the cache topologies of the different partitions and cancels any state transfer in progress.

But most of the time, the coordinator changing doesn't mean that there are multiple partitions, just that the old coordinator died. In that case there is a single cache topology, so there is nothing to reconcile and no reason to cancel the pending ST.

We can't rely on the new coordinator receiving a MergeView, because the old coordinator might have received a MergeView and died soon afterwards.