The case was shelved because no progress in tracking down Madeleine's abductor had been made.
Also, I think, Portuguese law (commendably in one respect) would not allow the unjust aspersion of 'arguido' to be hung around the necks of those accused (including Robert Murat) indefinitely.
The McCanns status of 'arguido' was rushed in just before a change in Portuguese law that would have forced the authorities to justify their reasons for imposing the status.
The McCanns announced their departure date.
The Portuguese chose to interview them before their departure date.
Because of what was to be covered, they were interviewed as arguidos, as per the legal requirements.
If you are implying that the McCanns chose a departure that they knew pre-dated a change in legal requirements, I'm going to ROFL.
If you think the McCanns would not have been made arguidos under the new requirement, we have plenty of evidence now that this is nonsense.