I'd imagine it's down to our convention of writing left to right, so more-related data points (such as properties of the same item) get arranged left to right.

I'd imagine it's down to our convention of writing left to right, so more-related data points (such as properties of the same item) get arranged left to right. A quick test to that hypothesis (which I'm too lazy to try to perform but offer to anyone who might be interested in looking or who might already know) would be looking at ancient Chinese table layouts. :)