A deep question that has been discussed for centuries. Perhaps the complexity is just a result of overthinking. The human mind or at least the intellectual thinking part of it likes to find reasons for everything. But chances are pretty damn big that the nature of nature does not work in the same way as our thinking.
Osho once put it like this:
“There is no purpose at all.
Life is purposeless. Don′t be shocked.
The whole idea of purpose is wrong - it comes out of greed. Life is a sheer joy, a playfulness, a fun, a laughter, to no purpose at all. Life is its own end, it has no other end. The moment you understand it you have understood what meditation is all about. It is living your life joyously, playfully, totally, and with no purpose at the end, with no purpose in view, no purpose there at all. Just like small children playing on the sea beach, collecting seashells and coloured stones - for what purpose?
There is no purpose at all.”
To not dismiss the word “purpose” completely, this says the only purpose is to experience life.
To me, this does not only make a lot of sense, but also increases appreciation and gratefulness for life, brings clarity and keeps things simple. It leaves us with one thing only, to make each day a better experience.