Shooting in studio gives the advantage of having total control of the light. You have a lot of uncontrolled light there, but like you said, it's all you got. It's been said that, "necessity is the mother of invention".
Why can one not have total control over the light outside? Granted, to be able to shoot in mid day sun AND control or overpower it takes powerful lighting... but it is possible and then no more difficult than shooting in a studio.
In fact, I find the constraints of shooting in a single room that always looks the same (no matter how many people you shoot)... boring and limiting.
Give me a simple alley way and I will be there all day taking shots in so many different ways and angles that you will think I was in 10 different locations, then I can move 1 street down or to the park across the street and do it all again!
The only factor there for me, is that I do not enjoy shooting in the rain. Some people do, and I know my camera could take it, this is just a personal choice for me.