Absence of evidence is of course not evidence of absence, but all life on earth today seems to be descended from a single organism, 3-4 billion years ago: https://en.m.wikipedia.org/wiki/Last_universal_common_ancest...

This is about a quarter of the lifetime of the universe ago, and we don’t have any evidence at all that life has ever occurred in any other way. We’ve only really been looking for a hundred years or so, but we’ve not found any “fountain of life” where life is being created, we’ve not found evidence of any type of life that isn’t broadly related.

I absolutely agree that it’s not evidence, but I believe that on balance, it makes more sense to take our working hypothesis to be something that fits the evidence we do have, rather than believing the evidence must exist we just don’t have it.

To be clear, I’m not advocating that we don’t investigate both possibilities, and I wouldn’t put much weight behind my own guess here.