In a way, the problem is of course not caused by the building regulations... well, not caused, but at least influenced by them. You simply need certain outdoor facilities and, due to the floor space index limit, a correspondingly large plot of land. But the large plot of land requires work, especially if you don’t have the money and/or the desire to install or have an irrigation system installed...
I can understand that you’d then prefer to cover everything with gravel. But that’s not the point.
I also have to say that I don’t understand the purpose of having 2 terraces. You can only ever sit on one... I don’t have 2 dining rooms either. And the bar in the kitchen... I already know that no one will ever sit there, it’s basically just decoration...