Because the world isn't "ending". Yes climate change might bring famine, destructive weather events, or plague but in the meantime we are living in the safest, healthiest, and most technologically advanced era of humanity up until now, especially for those of us living in democracies. Most diseases that would have killed you a few hundred years ago have been solved, in general there are very few wars (compared to the constant on and off warfare in history anyway), and in most of the world slavery has been eradicated.

Yes, there is societal divide (mostly due to economic difficulties and how social media influences people), yes there is bigotry and a rise in nationalism but much of this is only noticeable because of the media and the 24 hour news cycle. There has to be a constant issue hanging over our heads to make sure we are glued to our screens 24/7 improving shareholder value of the companies supplying the news on the current crisis.

So in conclusion, there are some global issues, but there is no reason not to go on an adventure, pursue that girl/boy you like, build a shed, or do whatever "side quest" you are up to at the moment. It's not like you're gonna solve climate change alone but you'll be completely miserable if that is all your life is about. The world is not ending for now, go do your side quests.