Dogs are traditionally good for two things: security and companionship. They are a great way to teach children responsiblity and provide them with a lively playmate. Somewhere in our evolutionary framework, we humans got it twisted.
In the last several decades, certain segments of the population have come to believe that our dogs are our children, and should be outfitted with sweaters, strollers, and Baby Bjorns. Gentrifiers don't have time for a conventional home life; they are too busy climbing that corporate ladder and living the dream of a fourteen-hour work day. Where do you think all that rent money comes from, son?
The choice isn't between a career and children; it's between children and career+dog-as-placeholder-child. Until we can engineer children to never outgrow a purse, this is a trend that likely won't go away.