Most people think saying sorry means exposing their vulnerability; giving power to the other which is why they don't.

I have a neighbour who swears she's never for once apologized to her husband in 18 years of marriage and the sad part is that she says it with pride.

Like you already said, saying sorry when you are wrong (and even when you aren't) means you are strong enough to let yourself be vulnerable and you value your relationship.

It's sad most people don't see it that way.