Forget statistics of past unrelated cases. Consider this case as unique. So, which are the physical, time and space possibilities of this person who opens a window to steal money or phones to abduct a child if he interprets the task as easy?
The motivation? Nobody can understand all the aspects of the human mind. Maybe he was scared to be recognized later, maybe he was also a paedo, maybe she shouted and he put his hand on her face asphyxiating her ...
But why losing time guessing about the thoughts of a person that is almost unknown to us? A human being could be able to think, feel and act in many ways unthinkable to us.
But you can say why thinking it was a burglary that went wrong? Because we have past and maybe RELATED cases: the thefts / attempt to theft in 5L, 5G, Casa Maria ... Plus "charity collectors" (also a type of crime which could be associated to burglary) at Casa da Aventura, Ashton, Cooper ...
So, my questions are: was Madeleine exposed to be snatched? It was physically possible? Forget the motivations of a dark human mind for a moment ...
I can assure you the motivations is the less important aspect of crime investigation ... Many times it is a mislead.