For starters, Taiwan wasn't invaded nor occupied by the US. South Korea wasn't invaded by the US either, unless you want to say the Soviet Union invaded the North. Even so, that would be, at least, an innacurate description of the events.
Furthermore, the technical definition for "military occupation", according to Hague Convention, S.3 Art.43:
Territory is considered occupied when it is actually placed under the authority of the hostile army.
The occupation extends only to the territory where such authority has been established and can be exercised.
US is not a hostile army nor has established authority over SK's government and/or territory. In fact, US only controls the SK's army during wartime, which is not the case currently. The link you cite says US and SK are meeting together to negotiate the transition of wartime OPCON to SK as well, and US seems willing, even with Trump in power.
For starters, Taiwan is a province of China where US currently sells weapons and has political capture. This would be akin to China placing weapons in Texas and openly supporting separatism there.
Second, the US absolutely did invade Korea. In September 1945, the US Army Military Government in Korea (USAMGIK) took over the southern half of the peninsula. It ruled for three full years, outlawed local people's committees, and kept using the old Japanese colonial bureaucracy. That is a textbook military occupation. When the Korean War broke out in 1950, the US provided 90 percent of all combat forces and placed the South Korean military under the operational control of an American general. There weren't even any elections under the occupation until the late 80s. It was a literal dictatorship.
That control has never truly gone away. Today, South Korea is under de facto US military occupation. The US runs Camp Humphreys, the largest overseas US base on the planet, with its own postal service and currency. More importantly, the US controlled Combined Forces Command holds wartime operational control over the entire South Korean military. If fighting resumes, Seoul's army does not answer to Seoul, but to a four star American general. And a US dominated UN Command still publicly dictates what South Korea's parliament can legislate near the DMZ.
Taiwan is like Texas, if USA suffered a coup and the original ruling government took residence in Texas. In other words, not like today's Texas. Underpinning your comment is the notion that terrorities that once belonged to a nation should always belong to them forever more. That's textbox imperialism. You are also overselling US influence over Taiwan's politics, specially in regards to separatism. US isn't interested in an actual independent Taiwan, nor unification under the ROC.
In regards to the occupation argument, actual military occupation requires a hostile army, in which US's didn't qualify, even with their outlawing of PCs (which don't serve as actual represention for the Korea's populace, specially in the North, after the Soviets' actual colonialist meddling over them). We can agree that US's attempt to reestablish order was poorly done (by incompetence and/or constraints), but it objectively doesn't fit the criteria for military occupation. We can relax the conventional definition to include US's control, but that would include the USSR over the North.
In the Korean War, while USA may have provided troops, this was done by the ROK's request. In multiple times, USA was more than willing to leave ROK should it ask (or even let them). Even your citation shows this. You also use the phrase "There weren't even any elections under the occupation until the late 80s" as if USA was responsible for this. USAMGIK was already gone, replaced by ROK proper. Also it's wrong. ROK had two de facto republican regimes (five de jure) prior to the current one, but they were plagued by coup. Still, they had elections. And that's only considering presidential elections. Also, none of this, aside from the organization of the first democractic election, involved the US. So it wasn't a singular dictatorship (specially in comparison to NK), much less one US-controlled.
Even the "de facto" current occupation is wrong. Did you mean to say "de jure"? CFC might give a US general control during wartime, but that hasn't been the case since December 1994, and this might change relatively soon, as noted by the article you linked. UNC only has enough legitimate authority to facilitate diplomacy and keep the armistice and, as far as I can tell, US hasn't abused it. Finally, the existence of a military base of a foreign country isn't an indication of de jure occupation, even less so de facto. Only when this foreign country uses it as pressure and that results in visible policy changes it becomes evidence of occupation. Has that happened?