Well first, it hasn't happened on earth because DNA-based life evolved. That serves to lock out other alternatives, because alternative organisms would have to deal with competition from DNA-based organisms while evolving.
Peter Watts wrote an interesting book, Arm of the Starfish, should give it a read. And it's worth noting he has a PhD and works with this stuff in his day job.
You're getting locked into a fallacy here, that evolution finds the best way. You must surely have noted that's not the case. We're running on a body template where we ingest solids, into our stomach, and that's directly next to our breathing tube, so sometimes the solids go down the wrong pipe and we die. And this happens literally thousands and thousands of times each year. It's a design flaw so unbelievably obvious it's on par with the Pinto's "gas tank in the trunk". But evolution is just concerned with "good enough".
The only thing you can know about things that didn't evolve is that they didn't evolve. That's literally it. Oh, and read the book (and Blindsight/Echopraxia). Brilliant author, diamond hard science fiction.