It's because Yihi will NOT sell the 350/350J to Chinese vendors. It's for foreign customers only, and with the advent of the SX Mini S and M, for Yihi use as well. If the Chinese mod makers want Yihi chips, they have the lower spec/lesser featured SX130, SX300, and SX330 series.
It's sort of a smart move, at the board's (tightly controlled) price point and with the market restrictions, it gives them something to compete directly with Evolv in the high end low production mod space, where the HEMO makers aren't directly competing with low cost versions from China. That helped the SX350 series gain a LOT of positive mindshare even before the J was rolled out.
Now all they need to do is score a coup and get one of the "big three" US Evolv partners to jump ship (Hana, Vaporshark, Vaporflask). I'm sure they've been trying to do this for some time, and lack of success last year led them to roll out the SX Mini instead. I'm sure at least one of those companies above are kicking themselves now for not signing with Yihi after all the DNA40 woes, and the sales and critical success of the SX Mini line (and corresponding loss of DNA40 mod sales).