Being seated in almost empty restaurants

It seems that almost every time we go to a restaurant that doesn't have many people there at the time we are seated near the other people. Why do they do that? I would prefer to be seated away from the other people so that we have more privacy. We have experienced this in a wide variety of restaurants.

Also, are there restaurants where you can just walk in and request a private room? I have tried searching and I can only find restaurants that require you to call so you can "plan your event".