It hasn't faded for 2 reasons, the first is historical grievances and the second is more recently events.

Japan occupied Korea, like you said, just less than 70 years ago, and historically that isn't a particularly long time ago, that is still in living memory for a few people. Add onto this the longer history, Japan has launched invasions of Korea before this, most notably in the late 16th century. Add onto this the general brutality of the latest Japanese occupation and issues like comfort women. These factors lead to bitter relations and it will take time for relations between the two countries to become less cold.

There have also been disputes since the end of the empire which haven't helped. Like other have said, the issue of comfort women is a big one. The Japanese government long ignored the issue and refused to acknowledge that military brothels existed, and refused to apologise to the surviving Korean women or pay compensation, and only started to reverse policy on this in 2008. There are also territorial disputes like the Liancourt rocks, which are currently occupied by Korea, but Japan claims them. This issue is more important than you would think, the South Korean President visited the Islands in 2012 and that caused Japan to withdraw its ambassador to South Korea for a while.

Theres still a general feeling of ill will between the countries, many forms of Japanese Media are still banned from Korea, like music. The two countries have tried to improve relations however, that was part of the reason South Korea and Japan jointly hosted the 2002 world cup. On the most important issues the two seem to agree however, Japan recognises South Korea as the legitimate owner of the whole peninsula, and both are concerned about North Korea in particular and to a slightly lesser extent China