Yes, preferences are a matter of taste, by definition. Yes, there is beauty and homeliness in every people, however defined. Yes, all definitions of peoples, by race, creed, ethnicity or what have you, are very nearly arbitrary. Yes, there are no sharp boundaries for any people, but rather Venn diagrams palimpesting to absurdity for the species. Yes, comeliness is not the best way to chose your couplings, but comeliness is the topic here.
All that said, there are a lot of comely women in Japan. I am avoiding 'cute', 'pretty' and 'beautiful', but using 'comely' to subsume them all. Japan's heteronormative male preferences in the media, and often in the individual, are for the cute at the expense of the beautiful, to the frequent extent of 'Lolita complex'. Understand not one word of Japanese but this you'll easily figure out watching any Japanese drama: the hot one is 'evil'; the cute one is 'good'; and as everywhere, the plain one is 'friend'.
It's not like I can put aside my preferences any better than anyone else. I have a thing for black silken hair and heavy-lidded eyes; whereas a colleague can't get over smaller tits. "So it goes..." I'd still say that Tokyo has far more comeliness than Toronto, even if Toronto has far more variety of it. Why should that be? Because nature is a bitch is why.
Before I was married I had dated 'white' and South Asian women from teens (when I was also!) to thirties, from one hundred to one hundred and fifty pounds. Over the half of my life I have used up I have coupled with East Asian women from ninety to one hundred and sixty pounds, from twenty to thirty-nine years old. Purely on the shallowest level, I have seen more attractive naked bodies on the East Asians. Yes, yes, I am hugely biased by my preference. Here's the thing: East Asians more often have their body fat spread more evenly, and an even layer of it under the skin. Others less so: Steatopygia. Subcutaneous fat hides a lot: wrinkles and cellulite. Who looks less wrinkled: the skinny old dude or the chubby one? Never noticed how smooth and youthful much East Asian skin looks? Subcutaneous fat. Never noticed even chubby East Asian women do not balloon in particular areas? And that Asian breasts seem part of, rather than attached to, their chests? Less steatopygia. These are just facts about populations, due to natural or sexual selection. Sure, you may well sexually select differently in ways not widely popular. I have a thing for namidabukuro. What's that about?!
So why is Japan pretty? Spread around body fat: makes a person look young twice as long, pretty much. Anything is else is preference. Well, even youthfulness is a preference, but nearly universal among men, straight, gay or flexible. Nature's a bitch.
Addendum: There's a discussion on plastic surgery in the comments, which is mostly against it, as my opinion is too apart from repairing significant injury or birth defect, such as a hare lip. Besides both subjects and surgeons consistently going too far, the tragedy of sameness, and probable psychological issues, humans cannot better nature. Look at the last picture. She's much too young for me, but I find her shockingly pretty. Would a surgeon have made that mouth a little too big, the lower lip a bit too plump compared to the top, the namidabukuro a little too large compared to the upper lids, the shoulders and wrists a bit too skeletal, and the forehead with such a high hairline? Never, but I would so do her. Gorgeous comes uniquely only.