In America, I found that it is exact opposite. Bathrooms are less in number compared to bedrooms. My son and daughter are fighting for bathroom time as we live in a 4 Bed 2 bath house. Adding to our agony was when my parents who recently visited us. Now, one bathroom for 4 people.
I understand the cost implications. But compared to my house in my motherland, American house is 3 times bigger. Why can't the builders reduce size and build more bathrooms.
> This is because we are always an extended family, and extended family visits us.
For most people in the US, this is not true. Also many bedrooms are never used as bedrooms; I am using a bedroom as an office right now and many people use bedrooms for storage or as hobby/craft rooms.
Often as the number of bedrooms increase there is an assumption that they won't all be used. So having a full bathroom for a guest room is a cost people usually don't want to incur while building. Or the house is built with the idea of parents (who get their own bathroom) and kids, who share and then move out when they're 18. Now that kids are living at home into their 30s, that becomes more awkward.
If you won't be using the extra bathroom, they become kind of annoying. I lived alone in a house with 3 bathrooms for a while. I felt like I had to keep a schedule to remind myself to use the out of the way one, otherwise the water would evaporate in the traps.