The biological burdens of reproduction are not and cannot be equitably distributed, so it is not unreasonable for the side with the higher burden to favor ritual displays of extra support from those on the lower-burden side, and not unreasonable for the lower-burden side to put forth greater effort in some areas.

It can be taken to excess, but it seems a perfectly reasonable custom which doesn't--unless taken to excess--need to have anything to do with power. Just recognition that we are not all identical. Displays of good faith can be useful to signal that despite non-identity we will sculpt our behavior to help make things more fair.