The problem with 3:2 is that it seldom, if ever, occurs in nature. There is a reason why paintings are seldom 3:2. It is either too oblong or not oblong enough.
Large format negs are usually either 5:4 or some kind of panoramic format and professional medium format 6x4.5, 6x6 or 6x7.
3:2 before 35 mm was mostly snapshot cameras like the box brownie and the folders. The reason for the 6x9 format was probably that you got 8 frames from the same roll film as the 12 frame square format Kodak A without anything extra going to waste.
I think that the familiarity with the format from using the box brownies made it easier to accept the small cameras, even if they were expensive.
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