Dont just look at the number, look at the size of the market.
PS4 accounts for over 1/3 of all hardware sales in the UK since 2014.
PS4 accounts for about 1/2 of all hardware sales in Germany since 2014.
PS4 accounts for under 1/4 of all hardware sales in Japan since 2014.
PS4 may have sold more in Japan than any individual European country but it represents a much smaller percentage of the overall market.
Which means Sony has more ability to grow in the japanese market than in Germany or UK.
Well Switch started completly owning Japan and Switch is in same time home console also, so PS4 grow in Japan would be very limited in any case.