Because there were people nearby and one of them would almost inevitably disturb him.
What people were nearby? You stated:
I think that, on opening that particular window and shutter from outside, the almost inevitable outcome was that he would be immediately disturbed, and therefore would not enter.
Nothing inevitable about being disturbed, was there? A slight to fair possibility, but he had an abundance of quite long periods when he would not have been disturbed. He was much less likely to have been disturbed, it is a possibility however
I think that it is dangerous to state things as almost facts, when they are not.
The danger is pegasus, that they become myths .... and given time and thousands of people reading them, they become "facts" ... and that is one of the ways Injustice happens.
I am sorry, I am being picky again, but I think it is an important point that stuff that we dont actually know, should NOT be presented as almost fact.