I think that the extended time needed is because the case may no longer be about just Madeleine, but also about other missing children by an organised and sophiticated set up. One with clout and an abundance of resources for spreading clever disinformation and an ability to change real facts, including Google Earth images.
I have seen GE images dramatically changed several times.
It could be an extortion racket, rather like the smaller version that Cristovao was running Procure a child and photograph the punter with him/her? Then the punter 'belongs' to the procurers for life.
I do not believe that Madeleine was abducted for this purpose however. Her aduction appears to be about very special bloodlines
Another reason for it all being such a lengthy process could be if the "owners" of the set-up are unbelievably important people. I have wondered if they are untouchables? Any charges would need to be more than watertight!!
All the above is only in my opinion