Cuba is a communist nation just 80 miles from the United States. Normalizing relations would allow its agents to work misanthropic acts in the United Sates. So the controls are a prophylaxis against communist subversion. China on the other hand is at a distance and too large to ignore. It is relatively harmless to ignore Cuba since it has little military or economic power, yet China with 1.3 billion people and a large nuclear weapons arsenal cannot be safely ignored.
Chinese Communism is one of two vast political threats to political and spiritual freedom remaining on the planet (the other is Muhammadism). With the end of the former Soviet Union Communist China presented the greatest challenge to free people in the political ideological battle between free people and government authoritarianism.
Communist Chinese leadership had begun moving toward limited free markets following the Nixon administration beginning at normalizing relations in order to move beyond the Vietnam War era paradigm with the Soviet Union investing in S.E. Asian and global political military intervention through arms supplies and military advisers. There may have been a divide and conquer element to the Kissinger-Nixon method since China and Russia had a certain mutual belligerency over Siberian-Chinese borders and leadership of the communist world.
At any rate the Chinese naturally moved toward limited free markets and relationship with the west over time because the free markets of free individuals is far more dynamic and productive than government owned and directed economics. China has other issues than those of political philosophy however; it has so many people that government discipline is required to keep the population from exploding and chaotic civil wars from breaking out- dynamic wars more of non-ideological demographics and economics rather than pure theory. It may be illuminated by saying China is like a tinder-dry barn full of hay and gasoline in barrels that requires government repression to keep fire from breaking out. A socialist-capitalist fight with light sabers in the barn wouldn’t really be good for anyone in China.
The worst thing about neo-communist China with its repressive government is abortion and the one-child per family policy that has existed for decades. China would have 3 or 4 billion people without it fairly quickly. The world cannot imagine what that would do; it’s really not good to think about because of the possible famines and etc.
I guess China will need to evolve a political economy with the best situation for individual rights, the best ecospheric restoration it can manage and good virtual reality for entertainment; in fact a healthy ecosphere with lots of wildlife would be entertainment for so many people too.
Cuba is likely to be moderately separated from the United States until China is no longer a repressive authoritarian threat to its own people and the free world. There are a lot of American sailors that would like to be able to legally sail to Cuban marinas and return normally. Sadly that will have to wait perhaps until all of the southern ocean reefs perish, dead zones expand so there are no fish in the sea and the waters become far more acidic.