What makes so positivity so worth it? And on the other hand why is negativity still around?
I think the key difference for positivity is the hope and belief that things will get better, thus we are ready to invest and create for the future.
Negativity on the other hand often times just feeds on that which has been created and believes everything is therefore limited.
Evolutionary basis and advantage in negative thinking is of course when people who think like that happen to be right. My guess would be actually that this capacity in built-in most of us under right circumstances: i.e.. when your basic needs are not met.
Same goes for positivity as well, when the circumstances are right we can focus to be more positive and long term thinkers.
Other people influence a lot to our lives and I think from the basic needs the feelings of psychological safety is quite tricky. We need social connections that accept us, yet we are also willing to adapt in order to fit in. Then again fitting in without getting accepted gets us into another dilemma and from these kinds of situations the negativity can emerge.
With this awareness we can start building more positive mindset in a long run.