I guess the important bit that always gets left out is that these things revolve around life as we know it. Of course you could have a completely different bioc

I guess the important bit that always gets left out is that these things revolve around life as we know it. Of course you could have a completely different biochemistry resemble the processes that we generally associate with life. But until we either replicate that in a lab or find signs of life on other planets (earth-like or otherwise), the best speculation we can do is based on what we see here. And we see that certain steps on the path towards complex multicellular life took very long compared to others.