You know... most people, or most reasonable people, would consider that to be a nonsense question. So already... I think the type of person who asks "why do humans exist" has already made assumptions that necessarily restrict the answer to a very narrow range of possibilities.
Of course... looking back, the OP is probably 12 years old, so it's not that bad. I'm just saying...
That answers how you are here but not why
"How does a person answer why something happens. For example aunt Minnie is in the hospital, why? Because she slipped on the ice and broke her hip. That satisfies people. But that wouldn't satisfy someone who came from another planet and knew nothing about things, first you need to understand why when you break your hip you go to the hospital. How do you go to the hospital when the hip is broken...
... when you explain a why, you have to be in some framework that you allow something to be true, otherwise you're perpetually asking why."
https://www.youtube.com/watch?v=MO0r930Sn_8&ab_channel=nebulajr
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And this is what makes the question ridiculous when a particular types of religious person asks the question. The type who has only ever considered the world through the lens of their religion has already made many assumptions about this framework such as creator gods exist and care a lot about humans.