I don't think DINK implies a lack of desire for children, rather the current state of not having any (and consequently a large amount of disposable income).

in my experience, people with large incomes often have more rooms in their house than they actually need for day-to-day life. sometimes it's just a flex, but often they expect to host their extended family and/or friends (and even their families) over the holidays. nobody needs a second kitchen and four extra bedrooms, but it does make bringing the whole family together under one roof a lot less tense.