We don't. But we know we can't replicate it, have never observed it, don't seem to find half-assed attempts at it in the wild and that there weren't multiple competing chemistries that found themselves co-existing, there was one.

I find it remarkable that chlamydia cells, fully enter host cells and live there stealing of resources.

I would call it evolutions “half-assed attempt” at endosymbiosis. (Disclaimer: evolution has no goal)