Frankly, because optimism is pretty much the only thing that has a chance of making the world of tomorrow better than the world of today. We have to be optimistic (while realist), there is no other way so future generations have a chance.

Turning off the news helps a lot as well imho. Our species isn't built to carry the weight of the world on our shoulders, and it deeply impact our mental health.

If I look locally, I find a lot of reasons to be optimistic