Not the poster, but I assume the idea is because a company of only young people often don't consider or understand the limitations/responsibilities of family life. Once you have kids, suddenly "corporate weekend trips!" and "hackathon all-nighters!" and even "beers after work on Friday!" become complicated commitments that require adjustments from the whole family. With a couple family-havers in the mix there is usually more acceptance of the work-life divide, or even that one exists (or should).

Because he goes home at night and has stuff to do thats not work and he isnt jealous of you for having that. Worst managers I ever worked for are divorced (and to an extent single) and hate seeing happily married employees