Why was Earthrise shot on Ektachrome?

If I was still on Twitter I would have asked why Earthrise was shot on Ektachrome?
E6 film dynamic range was (is?) sensitive down to 1/4-stop exposure increments as well as dev pushes (which labs could run with 1/4-stop precision if you did a clip test) so the chance of returning with an unusable roll was significant I would have thought?
C-41 film (colour neg) could easily take a four-stop overexposure and still retain range and detail.
Was Nasa thinking they could reshoot? Or was it that 120 (70mm with drive sprocket holes) format with low asa emulsion was going to give them the absolute maximum resolution? Did the Hasselblad have a mechanical auto-bracketing feature synched to the motor drive?
Any pointers from emulsion geeks out there v welcome:-)