Flying JL or NH the period of time I am on board is a respite from the destination/origin that is not Japan. The service level, the manners, the sophistication, and the food
The last thing I want is a non-Japanese FA. No thank you at all.
I think things have changed over the years. And there are three factors to address here.
Firstly, JAL has very high expectations of their cabin crews - Japanese or otherwise. This is why the initial Cabin Crew training for JAL takes three MONTHS verus three weeks for some airlines (although the average in the UK is around five weeks). Obviously when they recruit people they are also on the look out for certain kinds of behaviours that 'fit in' with the JAL culture. Training is completely Japan-centric.
Secondly, the main reason JAL had foreign based crews was because of the limited english most Japanese crew spoke. Although this has definitely changed in the last decade, most Japanese crew fifteen or so years ago spoke very, very small amounts of english. I flew JAL from Helsinki to Tokyo in December last year and the crew was entirely Japanese. And the crew member serving me had great english. So, things are changing there.
Thirdly, it's personal choice. I got a bit of a kick (in the best possible way) the first time I flew JAL to Sydney via Osaka around twenty years ago. The flight was ever so Japanese but it was also really interesting to see a couple british crew in the mix and from my experience, they fit in seamlessly in the business class cabin. Yet, they were also to offer to me what I like as a passenger from crew - banter. And banter is difficult with the Japanese crew. It really was the best of both worlds.