Well, we know life on earth is at least 3.7 billion years old, but it's not much clear how much older. Since the earth is 4.5 billion years old, that means that life could have appeared after ~17% of its life span so far, which is not THAT little. Furthermore, even if life appeared as early as the earliest estimate - just a few million years after the earth formed - we have no evidence that abiogenesis continued happening after an initial event, or that it happened anywhere except an initial location.

Those two factors may mean that abiogenesis could be an extremely unlikely event that randomly happened to occur very early in the Earth's life span.