Because geopolitically these are two totally different situations:
- Germany is surrounded by allies - Korea only has Japan.
- Bases in Germany aren't there for the defense of Germany (at least not mostly), but to cover other missions in the region (from your article)
Germany had been a key hub for securing missions in the Middle East and Africa, and especially in Afghanistan and Iraq.
Meanwhile the bases in Korea are there at most to defend Korea.
- At this moment the scenario of war with Russia is very unlikely and Russia would need to go through Poland. The combined armies of only these two EU & NATO countries, their mobilization potential, etc. would be bigger thenthan the RussianRussian equivalents. On the other side the Korean soil has seen over 1 million Chinese soldiers.
In general - Germany keeps those bases for political or tactical, but not for strategical reasons.