It's a nice idea, but given the starting salaries of post-docs and the lack of ability to control work-life balance in many places, simply handling the task of meeting the responsibilities of adulthood can be forestalled. Those who support us also have an expectation that at some point there is going to be a pay off. These things can interfere with the love of science, which is otherwise intact. Parents age, and would like to know they can one day rely on their children to be there with physical presence, and perhaps be financially stable enough to react to life events. As one example.
When the lifestyle interferes with meeting responsibilities, as can happen in a 5-10 year post-doc, the love of science starts to look like an indulgence. This is why people hope those elements will be different one day.