Because this wasn't a meeting of all of the bishops. That happens in June. The Cardinals can not make a decision for the whole assembly of bishops. Only the assembly of bishops can.
(Apostolic visitation = the bishop or his delegate going in and investigating, no?)
More like representatives from Rome investigating. That is, an outside investigation.
Why does it have to be 'proposed'?
So the bishops meeting in June can act upon it.
SD