Speaking anecdotally based on my conversations with SO who is a native Japanese speaker and very glued into internet culture. She's more liberal than most though.

It's not entirely true that AI is more popular in Japan. In fact, many creatives feel that the practice is in violation of Japan's much more strict copyright policies (compared to the US) and are seeking government action (which, so far, they are waffling back and forward on based on the week to week dynamics with the US. Weeks where the US footguns itself, they humor it again.) So in some respects, AI is a direct threat to the only power that modern Japan has in the global economy: soft power and intellectual property. They aren't the same Japan as the 80s, even cars aren't doing as well as they used to.

That being said, Japanese cultural dynamics are such that people are much more willing to "put up" with things instead of resistance. This creates the appearance of what people think is complete acceptance, but it's generally more complicated than that socially speaking. It's more a complacency to fall in line with how their employers or how their government feels about AI.

Government action toward AI is basically inexistent in most parts of the world right now, but I understand that a big part of this is US capitulation since the entire US economy is propped up by AI hype. Japan, much like Europe in the Ukraine situation, is unfortunately very dependent on the United States now for Oil due to the Strait of Hormuz closure and are not yet willing to do provocative action against US companies who are in definite blatant infringement of Japanese copyright laws. This has ruffled feathers of some activist politicians, but unfortunately Japan is very much losing it's own battle to the far right atm due to xenophobic spread of misinformation from AI generated anti foreigner rhetoric.

That's my understanding of the situation. And again, this is second hand and purely anecdotal discussion, but I think it's a bit more complicated than acceptance of generative AI and more a commentary on how acceptance works in Japan in the first place.