Geopolitics

I hear / read that it would be in both Japan's and South Korea's (SK for short) interest to be friends and/or allies. It's been acknowledged by both gov' and the USA wants it too (I think).

So why are they still not so friends ? Every military exercises where Japan and SK have to be together, they are actually "exercising with the USA", but not really together. And the list goes on of small stuff that could be improved on their diplomacy.

I hear it's because Japan did not make formal apology to SK for its past WW2 crimes, nor made any form of memory and introspection work on that period.

Why is Japan not doing it ? Why is Japan not working bigger on their relationship with SK when it's in their biggest interest in any matter (diplomatic, military, economic and whatnot) ?

Am I missing something ?