Often noticed that about late Victorian/Edwardian houses. Odd, isn't it? I can only suppose it's because, demographically speaking, families were huge at that point. Five, six, seven kids a commonplace thing. Close together in age, too. So I suppose you might have four or five people in the bathroom at the same time. By contrast, only one person was going to be in the kitchen — the mother of the house! Maybe a maidservant as well, if it was that kind of a family.
(Very into this mindset at present, because I am currently reading, for the third time in my life, the truly wonderful Lark Rise to Candleford, the memoir of a rural childhood in the eighties and then adolescence in the nineties — 1880s and 1890s, that is. I loved it at the age of nineteen, and still as much at my FOC age. In passing, you pick up a lot of social history from it, although it's the sense of a child's wonder and curiosity that comes over with a vividness that is unique in my reading experience. And she was a poor child, from a very poor family — of course, they had no bathroom at all. Cannot recommend it highly enough. Incidentally, it is not one jot sentimental, or nostalgic, contrary to what people think about it. Just very, very truthful and clear-eyed).