At what point does the null result in the search for ETI indicate our understanding of the fundamental nature of the Universe may be very incomplete? When should we conclude things just aren't making much sense?

Given what we've learned from Kepler, we know most stars have planets and something like 1 in 4 stars have a planet of the same size as Earth. Suppose in the not too distant future we identify 1 million planets the same size as Earth at roughly the same position in their system's habitable zone. And the ratio of surface land and sea water is roughly the same. But we never find any indication of intelligent activity on any of these planets.

That would seemingly put a damper on the probability that intelligent life some how emerged on Earth from naturally occurring organic compounds. It seems like it would also cause problems for panspermia theories, directed panspermia slightly less so but it still would seem unlikely at that point, at least to me.

At that point should we be convinced something is amiss? Does that leave us only with some variation of the Zoo Hypothesis? Would finding markers of unintelligent life on some subset of these planets be more or less confusing? Curious for your thoughts.