When you give a view to the window, it's for applying it only, ie. the window only has a read access to it. So its stores and return it as a const object.
If there was no const, you couldn't pass a const view to the window, then a lot of users would come here and complain "hey, why can't I pass my const view ? the window won't modify it, is it ?"
A small example :
class MyScene
{
public :
void Draw(sf::RenderWindow& Window) const
{
Window.SetView(myView); // --> COMPILE ERROR
Window.Draw(...);
}
private :
sf::View myView;
};
The ownership of the view is external, you have to handle it by yourself. RenderWindows just use your custom views, they are not meant to give full access to them.
By the way, if you don't need several views, you can just use the default view, which can be accessed for writing from the window.