Exactly, hotel lobbies are always full of people, coming and going, tourists, cuples, families, business people ecc... They don't stop anybody who gets in, I can just enter and go straight to the room without looking suspiciou, same think if an escort is visiting me.
In my opinion it's the best place for either outcall or incall. A studio/apt feels off, the same neighborhood, the same building of the same people, not the most discreet at all. I was curious to know why would people in Belgium prefer the latter instead of hotels.