Because the review task was still ongoing when the question got either closed or reopened. Now that the action is already completed, there is no point in continuing the review process for it - so the task gets invalidated to prevent further reviews. Review tasks are only ever marked as completed when the final review is what causes the action to actually take place.
So if you vote to close from review and that vote causes the question to get closed, the review task is marked as completed.
If you vote to close from the question page and that causes the question to get closed, the review task gets marked as invalidated.
The review queues operate by choosing posts which match a certain set of criteria and then creating a task for them. If those conditions are no longer met at some point (e.g. because the question got closed) then the system eventually removes the task because it doesn't qualify for the queue anymore. This happens across all queues and there are various criteria that can dequeue posts from each queue (see a somewhat outdated list).
All of this is done automatically by the system via the same processes that create the tasks. There is no button anyone, including staff, can push to just manually invalidate tasks with no other action.