That isn't somebody's home, that is a home which has been done up by a developer to a certain specification for a specific market: Middle Eastern buyers. If you have a look at the most expensive properties in London on Savill's and Knight Frank they all look the same and they all have a cinema room like that. Can see why a self contained house for the same market would logically have a hammam.
Doesn't matter a jot that it's not to our tastes. None of us could afford it. Nobody cares whether we like it or not.
Off topic. There is a Victorian Hammam which operates as a women's spa in my city and it's lurvely.