One of the easy answers to this question is because it isn't sexy and marketers don't know how to market it. High ISOs, details, and measurbations are all sexy--and since they're done in a lab everyone can talk about them and adore them.
Then folks who have little else to do can sit there and argue about their results on forums, in Facebook groups, etc. But it's an organic and real question that I've had in my mind for a very long time: Why don't we have cameras with lower ISO settings?. thephoblographer.com