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.
Even if a perpetrator has a specific modus operandi and signature every case is unique even if the outcome may appear to be similar.
By definition anyone committing the petty thefts which occurred in the Mark Warner complex was not very high up in the hierarchy of criminals.
Possibly young, certainly agile and possibly desperate on occasion particularly if stealing was to feed a drug habit.
He or she might have acted alone or may have acted with accomplices.
If insurance was involved there must have been police involvement and it seems to have been known to the complex management and staff that burglaries were happening.
If burglaries were endemic and if Mark Warner and the police were aware and treated each incidence as a petty crime they may have underestimated the seriousness of the situation.
Maybe it was thought stealing watches, cameras or even plasma screens was harmless and sustainable as items could be replaced without too much upset and without it becoming generally known.
It should have been a logical assumption that it was only a matter of time till the petty crimes escalated into something far more serious.
Whether by accident or by design is debatable ... but I would imagine anyone risking having his or her collar felt for the few euros petty burglary might realise could be tempted to consider how easy it might be to make thousands with just one 'big job'.