This has not happened once, it's happened multiple times in the Homo genus
None of those species developed the kind of representational, specifically human intelligence that builds spaceships and discovers universal gravitation. They "could have", of course, but as a poster up this thread has pointed out, we have left the hand-wavey philosophy behind and are now using the only way of knowing: the discipline of testing ideas by systematic observation, controlled experiment and Bayesian inference... this discipline is called "science".
We know of exactly one species that developed specifically human intelligence: us. There are tool-users all over the place. Tool-use is found in bonobos and birds. There are language-users of a kind as well: it would be astonishing if humans were so good at language if it wasn't an elaboration of capabilities that existed in our ancestors.
But what we do--specifically human intelligence, not the intelligence of beings who chipped flints into useful shapes or use sticks to capture ants or whose various articulations communicate a variety of important states--what we alone do is unique to us, and we are even beginning to understand why that is the case.
Obviously specifically human intelligence did not evolve to write sonnets or build spaceships, so it could not have been selected for due to its enormous problem-solving scope. Our brain uses 10% of our body's energy budget, which is a ridiculous burden, and it wasn't evolved against the possibility that one day it would be useful in the development of the political state. It was developed because it got us laid. Proto-human males and females were more likely to mate with partners who could entertain them, and being modestly bright themselves they found brighter partners more entertaining (this also explains why both males and females have the same intelligence, because both minds had to be engaged in the process for it to work.)
Quite accidentally, that resulted in our specifically human intelligence, which is not the intelligence of tool-using birds or communicative pack hunters, but the only kind of intelligence that builds spaceships and discovers mathematical laws describing reality (which is the only kind of intelligence the Drake Equation is concerned with.)
So all the actual evidence we have tells us that specifically human intelligence--not the intelligence of dolphins or whales--evolved:
a) by accident, as an epiphenomenon of sexual selection
b) exactly once.
Given the former, the latter is not surprising.
This is quite unlike every other complex characteristic of species. Eyes have evolved independently dozens of times (different types of eye use different biochemistry). Wings, likewise. Ditto fins. And so on.
So it is not at all implausible that the probability of developing specifically human intelligence of the kind required for a species to be detectable at stellar distances--a kind that is not found in any other species on Earth--is extremely improbable, even though life itself is extremely probable. And that is my personal bet, as we go out and explore other worlds: we will find life everywhere, and the specifically human intelligence that took us to the stars in the first place... no where.
[I've had this argument before, and am not under any illusions as to the ability of people who believe intelligence must be common to bring up imaginary "counter arguments", but what we can or cannot imagine has no bearing on what is real, only reality does.]