Our marriage isn't very couple-centric either, but I think that's completely independent of polyamory. We're just both very independent individuals. We're both pretty selfish. It just so happens that one thing that brings me joy is seeing my husband happy, and vice-versa, so that works out well.
I believe there was a phase in there somewhere that we were a little more "we" than "he and I." Perhaps it's something that a lot of people go through, before growing out of? And I totally get how having kids forces that "growing out" stage to include "kids growing up." i.e. it's not uncommon for people to face Empty Nest Syndrome and then be forced to basically re-invent their marriage and their individual selves to accommodate the new found freedom from responsibility?
As it relates to polyamory, I think it could definitely be a "we" stage in dating. Some people aren't ready to deal with their partner going out on their own, dating solo. So dating as a couple is a way to bridge that gap, dip your toes in the water without letting go of the life preserver that is your spouse. Just a thought...
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker