Because of the view, position and huge screens, where most of the matches are projected. Also the soft grass is simply the best invitation for summer picnics or any kind of outdoor activities.
Especially during the sunny days, this is a must see! The view is one of the best You will encounter in Prague. This is the place, where You will realise why Prague is called the city of hundred towers,)
Go to the top of the hill and check out the view! One of the best.)