kids and their big mansion

Today, I went to my new student's house. It was a big house but she only lives with her mom. Between what she says, I get the feeling that the father is not of a strong presence in the house. There are many families like them in Canada where the father is working in Asia but the mother stays with the child in Canada. It's become quite a norm. Question is why do they need to buy such a big mansion for just two people?