Well, I was bored and couldn't find the answer. So, I made a list of sizes using both inch and metric numbers:
There are some sizes for which I did not have the metric/inch equivalents. I don't believe they are necessary to understand my hypotheses.
First, the 2:1 ratio may be an artifact of sampling. Although a lot of sizes fit that pattern, a lot do not fit it.
Second, a hypothetical "804" converted to metric would be a 2010. Since the 2010 is a recognized inch size, it may have been decided to avoid potential confusion and make it an 805, which in metric is a 2012.
Third, things just happen, and the engineers weren't even thinking about the apparent pattern in aspect ratios at the time.
John
PS: I can't get the table to post. See the attachment.