There's likely no natural reason "why" we exist. Scientists answer "how" questions, not "why" ones. So the natural story will be the evolutionary one of how we came to be here, and how life generally is created.

But then there's the question of the emergence of higher-level properties and patterns that we can model with our philosophical and even religious abstractions. Those models will all be inaccurate generalizations or idealizations, but that doesn't mean they're powerless. Our abstractions might have higher-level functions, motivating us to behave in certain ways. Or they might be epiphenomenal illusions.

For example, the theological abstractions often have political functions, in that they're meant to organize society and to provide excuses for certain tribal prejudices and economic inequalities.

One question, then, if we're going to have to tell some such inaccurate philosophical story to supplement the stripped-down scientific one, is what the least embarrassing model or narrative might be, about what we should do or why we're here. That narrative would be judged largely in aesthetic terms: how creative is the philosophical story or myth, and how inspiring is it as a work of art made of ideas? That might be the most enlightened approach to our search for meaning.