The police don't have the resources to keep missing person cases live, they will only do so if specific leads become available to them. The Maddie case is only alive because certain influential individuals have exerted pressure upon the authorities to do so while other missing child cases are effectively abandoned.
I think you are wrong, Angelo.
Investigation into missing children cases continue for as long as there is evidence to be followed and are only 'effectively abandoned' when all active leads have petered out; unless or until new information comes to light which merits a fresh look at the investigation.
Which is what happened when two independent reviews were conducted into Madeleine McCann's archived case.
The case was reopened because evidence which had not been investigated was found; the fact they are still working on it suggests they haven't yet exhausted their enquiries into that evidence.
I suppose that could be considered expanding the investigation although in effect I think it was merely picking up the ball which had been put down and running with it.