Gee, how come?

Gee, How come some people treat others so disrespectfully?
Today I was at the local grocery store.  The store is not too large, so while making the rounds, you sometimes see the same people as we weave in and out of the aisles.  This happened today with two couples-male and female.
Couple #1 were both in their maybe 80's.  He was pushing the cart, she was choosing items and putting them very tentatively into the cart. Sometimes he said nothing, other times as she worriedly looked at him, he told her that was wrong, put it back.  No kindness in his tone. Sometimes, she would place her hand on an item and look at him for guidance.  He would say, I don't know, you should know.  When I was coming down another aisle, he made an abrupt turn, almost colliding with another cart and me.  He very pleasantly joked with me that the aisles are too narrow-he was correct, but he treated me, a stranger very politely.
Couple #2 I encountered in the area where you choose which cashier lane you will go in.  They were in maybe their 60's.  He was telling her over and over which lane to put the cart into to queue up. But, she wanted to get a few more items she said, he said no, that is all we are doing, now get in that line-very roughly.  He continued negative comments to her even while he placed the items on the conveyor belt.  The items were placed very precisely, if they wobbled when the belt moved, he methodically aligned each item again, still talking to his wife.
So, here I am judging and wondering again.  I wonder what the situation was with Couple #1?  Was she having memory problems, and could not make proper choices for items that once gave her no problem?  Was he not used to going with her to the store and felt out of his element and needed to show resentment to hide his lack of knowledge for grocery shopping?  Was he always so domineering?  Was she always so tentative to make her choices freely?  I don't know, I am outside of their lives, do not know what brought them to this place.  I could only see that they both were unhappy and stressed.  It saddened me greatly.
Couple #2 made me mad, why were all the decisions his?  Why did he need to continue to beat the dead horse?  And, why is she  taking that constant assault on her self respect?
Again, I do not know what their dynamics are outside of that store, that day, I only know it was hard to listen to for me.
Life is short, life is hard, life is a gift, relationships are gifts.
Please let's try harder not to always say negative things to those we hold so close. It does not all roll off the back,sometimes the constancy of the statements start  a fissure, and all future unkindness sink in to fill whatever space was formerly occupied by who we felt we were. I think one of the main reasons I had so much difficulty in my first marriage was because the statement "I was only kidding" was used to defend cruelty to all family members.
My accusations and advice are finished.  I need to make sure that I can also not be accused of doing the same things.