Why do bees fly inside the gaps between the decoration on the exterior wall of a building and the wall?
They just want to escape from.the heat. If there are no trees near your area, the bees can make a hive to live in. The bees don't constantly fly around; they only do so to gather food (or looking for a partner to mate).
Regarding the particular side of window, I'm not sure, may be that part is a little dry or (damp). What I mean is that the microenvironment of that crack may be more likeable to the bees, though that is just my wild guess.
Hope you found your answer. Thanks for reading.