Because it's too much of a lift at once. To naturally get a mirror E-Coli you'd need a separate planet and billions of years and lots of luck.

It's a mostly-incompatible change to all the machinery all the way down.

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gs17 a day ago | parent [-]

I could see "semi-mirror" life evolving step-by-step. There's a few microbes that can eat L-Glucose already (although the enzymes involved seem to be meant for other compounds and just happen to work for it), they just aren't taking advantage of it yet.

	▲	Terr_ a day ago \| parent [-]
		That's a far cry from, say, developing reversed DNA and reversed DNA polymerase and all the other transformative and/or structural proteins of the cell. It's not just about the food/excretions of the hypothetical cell, but about whether its structure and innards are things the rest of the ecology can detect/defend-against/consume.