Intelligent life most like arose from the extinction level events that wiped out less intelligent super predators. This gave those who are far weaker but with higher brain capacity the chance to express their genetic variations.
Dark forest hypothesis explains this in a “dark” way. They exist but are smart enough to hide from hostile hunter/predator life forms. Meanwhile our dumbasses are blasting radio signals into space like a little kid trying to talk to every stranger they see.
Interestingly we can’t actually know that we are correct in our calculations of what a planet lightyears away has as its atmosphere because we will never be able to go there and make sure we are correct. It’s a calculation and nothing more. For all we know that planet may not even exist. That’s what’s mind blowing about astronomy. We really don’t have any way of proving anything about what we are observing. All we can say is we are observing. That’s the only thing science can offer us.