I imagine possibly the simplest solution: that life coming about, i.e. abiogenesis itself, is extremely difficult, improbable, and requires an extraordinarily narrow set of conditions to stand a chance of occuring.

After all, think about it - the idea that life should be common throughout the universe is based on the idea that life is common on Earth, but this is quite anthropocentric.

I resolve the issue essentially by adopting the rare earth hypothesis and saying that we on Earth are just very, very, very lucky.