Not concentrating on localization and expanding their TAM.
Japanese firms had much less money to play around with after the Asian financial crisis in the 1990s, and localization costs a LOT of money.
Japan is already a large (125M+ pop, $4T GDP) market with an insular population that only really speaks Japanese.
This meant Japanese companies line Sony, Toshiba, etc can survive by just selling to Japanese customers without having to worry about spending money on innovating or building competitive products, as non-Japanese companies didn't care as much about Japanese localization and Japanese consumers couldn't really afford dollar denominated products on a Japanese salary.
Within 15 years, Japan got overshadowed by Korea, which to Japanese before rhe 2010s was what Americans think of Mexico. Korea has a much smaller population and historically had a much poorer population than Japan (they only caught up in median household incomes recently-ish - last 5 years), and as such Korean companies were more international facing and open to adopting best practices from abroad and competing in the developing world (it was Korean companies like Samsung that paved the path for Apple to begin manufacturing in China, India, and Vietnam)
Companies like Sony, Toyota, and Kirin got overshadowed by Samsung (Korea), Hyundai (Korea), and Lotte (Korea), and Korean conglomerates like Lotte began buying up Japanese prestige brands, and even Japanese-Koreans became like Mayoshi Son major titans of industry