Why do program committee meetings often take place during the weekend? Because people have other work commitments during the week, and it is hard to get them all together at the same time.
But what about family commitments? Those don't count. People have some flexibility and can always shift things around, it is assumed.
Why can't people shift things around at work as well? Because some of those are hard constraints.
But at home also, some constraints are hard: of a child is performing on a school play for example, that cannot be moved to another date.
I think that there is an unspoken assumption that gives priority to work over family time.