The watch and cash are easily concealed and disposed of. A person stealing them is just a person leaving an apartment. A stranger stealing a sleeping child, negotiating doors and windows with the child, and not being seen by the child's parents and friends is a more difficult proposition and far more likely to leave evidence. This is especially so when the stranger is in the child's room, opening windows and perhaps exiting via a window. All the while, people who know the child regularly check on her and her siblings. It's just not the same proposition.