Mitsubishi says the following about their first model in 1988 which was square:
(translated from the original Japanese)
Keep in mind that a non-circular shape can still be pretty symmetric. Consider a rice cooker shaped like a hyperellipse, for example. Now, “不均斉” is supposed to be good in Japanese aesthetics but I have no idea if manufacturers of electronic rice cookers care about that versus making the gadget look “modern”.
And I also note that even in the most lopsidedly asymmetrical rice cooker, the actual bowl is still a perfect circle*, because I assume it’s hard to guarantee even heating otherwise.
*At least, in the relative few I’ve encountered at close range.