I ask again, how do you know none of the 10 people had an inkling?
To answer your question, the recon was about discovering what happened to Madeleine and regardless of where that journey took them, the police had a moral duty to pursue it.
OK - I'm going to try once more. If the reconstruction was about trying to find Madeleine it would have failed especially if all of those taking part had no idea what had happened and all that was being re-enacted were the movements of a bunch of innocent people coming and going. Even if some of the participants HAD known what had happened, the reconstruction isn't suddenly going to go left-field with one of them re-enacting hiding a child's corpse along the way (I wouldn't have thought).
If the reconstruction was about trying to find evidence of wrong-doing by one or more of the group it would have failed also, because how would the police be able to state categorically that any glaring inconsistencies in the timeline re-enactment were not simply down to honest human memory failure? A reconstruction of the movements of these people as per their witness statements isn't suddenly going to shed light on the identity of Smithman is it? Or show Madeleine falling off a sofa, in a Calpol induced haze fgs.
The McCanns friends would almost certainly have come to the conclusions that I have come to above and therefore questioned the validity of the whole exercise. They would have seen it for what it was - a last ditch attempt to try and scrape together a case against the arguidos and on that basis who can blame them for not wanting to take part. If any of them genuinely thought a reconstruction would have helped Madeleine I've no doubt they would have been there in an instant.