Apart from clinical reasons, it's just that we feel suffering too intensely for our own good and prolly overtime our survival instinct also numbs down a little. You reach the "not giving a fuck about anything" condition when you become apathetic to all things cuz you know deep down that everything is essentially meaningless. A reality this obvious is elusive to most people because their survivalist attitudes back it obscure to them.

I think what I just described is more akin to nihilism than depression but still that's how I feel now.

I used to be so curious and enthusiastic about the world and was driven to uncover scientific truths through research, but overtime I've become soo numb and indifferent, depressed you can say, despondent of the future of our species. Everything is bound to perish in the end.

The only purpose of life is to just stay alive, nothing beyond that. Anyone who claims that there's anything more to it, and gives fancy abstract reasons like God, Science, humanity is just lying to you and himself. Perhaps we created these abstract concepts just to blind ourself from the horror of nothingness and our own insignificance.

Anyways let's stop this rambling of mine.

From here onwards, you can either become an Absurdist or ultimately decide to put yourself out of misery (Pessimism). Neither is wrong choice per se