For one yes the national age of consent in Japan was 13 but this never really mattered and nothing really changed anyway because most Japanese prefectures just like US states have their own local laws and most prefectures actually have the AOC from 16-18 so in reality nothing really changed.
Second regarding the age of majority they did this mainly because Japan's working population has been shrinking in recent years so one way they tried to get young people back into the workforce was to give Japanese teens more responsibility such as they now have the ability to get an apartment in their name apply for loans and credit cards and even get married without their parents permission.
The Japanese government wants young people to spend more money contribute to the economy and work hard because in Japan if you don't work or have no direction in life you are seen as a loser as they say "出る釘は打たれる" The Nail that sticks up gets hammered in.
However from what i have read on this topic some Japanese argue that even though they are now legally adults they still don't really feel like it and also, don't like that the new laws have a negative impact on Coming of age day which is the day Japanese people celebrate when someone turns 20 or an adult pre-2022.
Just thought i would give some context here and add some clarification.
