<< So in case you accidently open one that is occupado, you don't get a view of something that you wouldn't want to see 🙂 >>
I would say that, plus 2 more reasons:
1) If opened from the outside by someone, you could stop them from actually entering by holding the door closed. Gives you more control and privacy.
&
2) If it opened outward, you have the chance of opening the door on someone that might be walking around out there. By making the door open inward, there is no reason to figure out the clearence of the door so it can swing freely and it makes the stall a completely self contained unit.
<------May be putting too much thought into this.