A turtle on the Galápagos Islands in 1450AD could use the same reasoning to conclude that no seafaring civilizations existed.
Also, since he’s a turtle, he doesn’t, presumably, yet actually know how hard it is to make a boat. The argument for determining whether or not you are the only seafaring species depends, first, on you having attained the ability to travel the seas…
All of that seems necessary before he can conclude whether or not he should consider it ‘surprisingly late’ for his island not to have been reached yet by any seafarers.
But the interesting part of the analogy is maybe that the turtle might fool himself into thinking he understands the parameters well enough to estimate this probability - after all, he’s paddled around off the beach and even made it to a nearby rock - so he reckons he’s got a pretty good handle on how hard it must be to travel between islands.
Ignorance and misestimation of the true underlying factors isn't a trait unique to these hypothetical turtles.
Or, perhaps you have a much higher confidence than I do in humans' assessment of the factors involved in your questions.
I'm saying we are over-confident in the underlying premises of our understanding, just like the turtles would be. The more of the questions you pose that go partly unsolved, the more unsubstantiated the conclusion. Their probability calculations are pointless -- garbage in, garbage out. As demonstrated by the patent wrongness of their conclusion.
If you are confident that we've got solid answers to the interstellar corollaries of all your questions with the evidence we can gather at this point, then we aren't on the same page at all.
This idea, that our observations of the universe are a properly representative sample from which to form conclusions about the unobserved universe, makes as much sense to me as the thinking-turtles assuming you need a small green island to and a thick shell to enable sentience because that's what their observations show.
Certainly no-one would make the claim that "there are (definitely) no aliens in the galaxy" when we can't disprove the idea that aliens traveling at the speed of light just reached the galaxy (with our current understanding of physics). That doesn't mean you can't make the claim "there are (almost definitely) no aliens in the galaxy (because I just created the most amazing telescope ever and looked at every particle of matter in the galaxy and there were no aliens there)". The principle of charity demands that understand the bare claim that "there are no aliens in the galaxy" to mean something that is plausible, such as "there are almost certainly no aliens in the galaxy".
Well, what matters is expectation. The fact that some people win the lottery doesn't prove that playing the lotto is profitable. In fact it isn't money-profitable. The fact that people sometimes win doesn't change the nature of reality, that even for them, the win is unexpected and playing was negative expectation for them.
You seem to be confusing expected value with results.
Do you revise your decision process every time you get unlucky? On a meta level, sure, paying attention to unexpected failures is important to look for systematic errors. But randomly getting unlucky on 99% certainties does not automatically disprove your decision method.
For example, when asked to be more granular, the turtle could say 'I reason that there is only a 1 in 10 chance that seafaring civilizations exist'. The existence of seafaring civilizations doesn't make the turtle wrong in this case.
If the turtle concluded that 'there can not possibly be any seafaring civilizations, because I don't see any' then you could accuse it of bad reasoning.
The hypothetical turtle did exactly that, loyally following suit with the commenter who I replied to.