The guy on cool worlds YouTube channel (Department of Astronomy, Colombia) has argued that we're still in the early days. The conditions for intelligent life in the galaxy hasn't been around for that long.
We could already colonize Antarctica, or the sea-- those are easier to reach, supply and colonize than other planets, but we are not trying.
Most of our past exploration/settling efforts happened because there was some gain to be had; it seems quite plausible (if somewhat bleak) to me that interstellar travel could just remain pointlessly expensive regardless of technological progress.
On the other hand - we were and still are present on the Antarctica, have a permanent base on the South Pole etc.
And even if these aliens have cracked FTL travel, who's ever going to find our little planet on the ass end of some mediocre galaxy, with an EM emissions bubble that has only covered 100 light years so far? Needle in a haystack.
They could have been here already before modern humans even existed.
Perhaps it's much more likely to have happened elsewhere in the galaxy 4 more billion years from now. If I remember correctly, stars with our particular properties haven't been around for too long.
I recommend looking into cool worlds lab since you seem to like inferring from the numbers.
Luna is sort of made from the Earth. And it's so close that Earth has a stronger pull on it than Sun.
So we have set foot on another stellar body, sure. But we also... kind of haven't.
And then we had to retreat from it anyway. Homo sapiens, hunter champions, arrived at an uninhabited body and were outmatched.
Way to go, smartest species we know of. You've done jack shit.
The second reason is to escape the death of your own sun. That takes long enough that far fewer lifeforms would be expected to even face that challenge compared to resource scarcity. If you manage to sustain a high-level civilization that can overcome resource scarcity and conquer the challenges of interstellar travel for the billions of years it takes a star to die, maybe you can simply prevent that death by technological means we could not possibly foresee or understand?
Those are hand-wavy answers, but this is sort of the problem. We're imagining near god-like beings here and asking why they don't behave the way humans have historically behaved with respect to exploring and colonizing remote parts of our own planet. The analogy breaks down at some point and we have no idea what beings capable of that kind of thing would even want to do.
Even our best sci-fi imagines answers that are pulled out of imaginary asses but frankly no less plausible than anything else anyone here will come up with. The builders of the expanse series expanded to a few hundred systems but then simply didn't need to expand any further. They figured out how to stop fusion and star-aging and tapped into energy sources from other universes (then got killed off anyway, but seemingly would not have kept expanding). The monolith aliens of the space odyssey series evolved into a non-material form that was actually here the whole time but we had no means of detecting them.