It is because of separateness.
Separateness means we are all separate, even when connected.
It means we would naturally have our own separate opinions (and thoughts, concerns, desires, wishes, goals, etc). Separateness just is. Connections with others doesn't negate separateness. It can't, because separateness just is.

Others who don't get separateness, may think that their thoughts should be our thoughts, and when we don't respond to their thoughts (because we have our own thoughts), they may label that in some way (wrong, stubborn, selfish...).

They may get angry with us but it's pretty silly to get angry because another person is separate, with their own thoughts. They may get frustrated too, and their frustration comes from their thinking that we should respond to their thoughts, that they can't control that; this frustration is about them, their inability to understand.. separateness.

Separateness is something I work on a lot, and I try to keep it in my awareness to learn more about how it works with me and with others.

I honor your separateness and your opinion