Probably a mix between oil-ties and the fact that decisions in Japan are made slowly.

Edit: I also think there's a fear of this: wide acceptance of EVs open the door to BYD (or similar) huge takeover of the car market.

Japan is slowly decreasing it's oil imports,they consume now 30% less oil than in 2003.

https://opengov.jp/en/economy/energy/crude-oil-imports/

Japan (Panasonic) is important baterry cell manufacturer, but most battery cells are exported, not used for domestic EVs. For example Panasonic is supplying batteries for Tesla.

https://en.wikipedia.org/wiki/List_of_electric_vehicle_batte...