The distinction that I see is that work should allow people to balance life and work life, regardless if the reason people need concessions are children or because other reasons. It is also a sad fact that in many cases there are social stigma attached to those reasons and thus make it likely to be concealed. What get perceived as choice can actually one of those situation which a person has not chosen. To put a number to those things, about 50% of the population is currently suffering from a chronic diseases. You add that with the number of people who has elderly relatives, the number of people with children, and the total number is creeping very fast towards almost 100%.

It is also a bit telling that in a very large company in my country, the term used for flex work can be roughly translated to "entrusted work schedule". It seems that the reason people are not given concessions automatically is that the employer simply don't trust their employees and view flexibility as something that a stereotyped lazy employee will abuse to goof off and play video games. A good start to combat this would be to view flex time as something that everyone need, which would naturally benefit parents.