Aren’t the fact that there are other gases that we breathe in with oxygen reason we live, like how oxygen is highly reactive so breathing pure oxygen in big quantity will cause reactions in our body and kill us, and other gases (nitrogen mostly) act as a, so to speak, barrier against those reactions.

Also, I understand that if there are bigger concentration of oxygen we could adapt and survive, but also like too much oxygen (whatever that amount may be) can also cause to not live and different form of life to exist instead