Patron, you're exactly right. I would add that incall locations can be apartments, condos, or even suburban houses--in other words, they're often in neighborhoods. Neighbors can get suspicious about a steady flow of single men showing up day and night at a house or apartment, and those neighbors have an investment, literally, in having a safe, quiet neighborhood or apartment building. Incalls are sites of ongoing activity that can be considered undesirable and perhaps criminal. People come and go all the time in hotels, and having a well-behaved guest is nothing that the front desk or other hotel guests will care about or usually notice.
I'm not saying that Montreal incalls aren't safe; I'm sure they are. But I agree with Patron: outcalls, when handled correctly, are safer.