IMO other uke dealers get more coverage because of video podcasts, the way they do their "sound samples" (essentially mini-concerts from Kalei/Corey) & wider range of price points. In the case of HMS, their bricks & mortar shops aren't in HNL/Waikiki, so likely fewer Japanese-speaking foot traffic. And if there are Corey speaks Japanese, I think.
If one's customers don't speak/read your language, it'd be in one's best interest to speak/write theirs. HNL is "just" a 7+ hour flight from Tokyo.
Japanese tourism is significant & distinct enough that it gets its own "category", like Canada, eh? ;-).
Official Hawaii visitor stats are broken down into U.S. West, U.S. East, Canada, Japan & "All Other International Markets".
Writing from my limited experience w/ Hawaii.
Years ago, I was the only non-Japanese person in a shuttle van in Waikiki in Honolulu, besides the driver/guide. The blonde surfer-dude-driver-guide spoke to us passengers only in Japanese... probably because I probably blended in, appearance-wise, LOL. Besides the guide, I think I was the only fluent English speaker. And can't speak/read Japanese...
Waikiki is as vacation-touristy as it gets in Honolulu, & Honolulu is as touristy as it gets for Hawaii... & Hawaii is as (arguably) touristy (& conference-y) as it gets for the US. Vacationers spend a lot of disposable income & vacationers from Japan consistently (likely over decades)
have spent the most, as a demographic. Very generally speaking, the demographic that can afford a HNL/Waikiki vacay are likely going to be the pool who can go for a big "K" brand. There's something like 5 ukulele shops just in Waikiki, not counting the one inside the Hilton Hawaiian Village complex, which might even get enough sales just from HHV guests alone. Most visitors from Japan stay on Oahu. Japan also has a deeper/longer history w/ Hawaii & luthier-grade musical instruments than other Asian countries.
Tourism from China, while very, very significant in recent years ("newer" money, relative to Japan), might be more variable (especially nowadays... travel warnings, trade war/presidential politics, etc). Also, generally speaking, there's cultural differences (what is purchased) between tourists from the two different countries, generally speaking.
A very loose analogy could be Japanese vacationers in Waikiki are kinda sorta like residents of Chinese/Hong Kong/Taiwan-to-a-lesser-degree-descent, in Richmond BC. In my opinion & observation...