You obviously didn't read Brietta's post properly or understand her point:
"Sometimes individuals may be in possession of information which they may have no idea may be of value to an inquiry"
If they don't think they have anything of value to bring to the investigation then that would explain why they haven't come forward to claim any reward.
The OP
'Police are searching for a resort worker who they claim 'kept secrets' from them during the initial investigation into Madeleine McCann's disappearance.
An insider has revealed officers are searching for a Portuguese man who was nearby when the three-year-old went missing while on holiday in the Ocean Club resort in Praia da Luz, Portugal, in 2007.
A Portuguese police source told the Daily Mirror: ‘This Portuguese man used to work at the club resort, he speaks a bit of English.'
'Kept secrets'. That certainly sounds as if he knew the value of the information sought.