Many rulers in ancient China did conflicting things. They wanted help from people but never trusted them. A good example would be Liu Bei. He desperately wanted Zhuge Liang's help, but he also worried about Zhuge Liang taking too much of his power. People say that the main reason that Liu Bei decided to take out his million troops to avenge Guan Yu's death was to take the military command from Zhuge Liang. And even when on his death bed and when he even more desperately needed Zhuge Liang's assistance to help his incompetent son, Liu Bei tested Zhuge Liang for his loyalty and was ready to kill Zhuge Liang at moment's notice. And Zhuge Liang knew it. That's why he got so scared and immediately swore his loyalty to Liu and his son.
The CCP may have a similar syndrome here. The Chinese govn't wants these scientists because of their scientific training in the West. They are also aware that living in the West for so long also gives these scientists something else: the idea of free thinking and possibly even a belief in democracy. I would think one thing the govn't worries about is that these Western trained scientists may bring the idea of democracy with them. And we know how much the CCP "loves" democracy. So it would be impossible for the govn't to completely trust these "sea turtles". Giving them too much voice might risk some of them finally convincing the public that democracy is a good thing for China. At least, that would be one of the things that the CCP might worry about. So don't expect to be fully trusted by the govn't if you decide to go back. They shake your hands and even hug you, but they also keep an eye on you and make sure you don't say/do things out of line. The same thing happened before. In the 50's, many overseas Chinese came back to contribute to the development of the new China. At the time, the Chinese govn't also understood that they needed help and the education and experience that these scientists brought with them were invaluable. That's why they were welcomed with open arms and intensively advertised as a sign of the power and the attractiveness of the newly formed communist China. And guess what, many of these young scientists became some of the main targets in virtually all movements in China, including the cultural revolution. Many of them were suspected of spying. It just shows you how much they were trusted by the govn't.
Also nominating people to the national academy of sciences is not the job of the govn't. It was the scientists themselves who do that. It is highly possible that many existing members on the committee got jealous and feel threatened by these "sea turtles". They, in turn, wanted to show these see turtles who's the boss by not electing them. Note that all I was trying to explain was why these brilliant scientists were not elected to the national academy of sciences.
Things like this happens a lot in China. My own parents got similar treatment when they were working in China. My dad was publishing a lot of papers and was getting some serious attention in his field of research. His boss got jealous and kicked him off the team and told him that he could never do the same kind of research again. And my dad got harrassed no matter what else he wanted to do. It could be that they stopped ordering chemicals that he needed to do his experiments, or some of his instruments got moved away. My dad went so desperate he wanted to switch to theoretical physics because this is the one field that does not need any chemicals or equipment and he won't need any permission from his boss to do his research. That was also part of the reason that my dad eventually decided to come the States. AND when my mom wanted to come the States to visit my dad, she was thinking retiring early to keep her benefits with the Institute. This was a common practice at the time and everybody did it. but she could never get permission to retire. In the end, my mom had to quit and give up everything she and my dad earned while working there for 20+ years. Guess why? My dad's old boss was the head of the Institute and he was giving my mom a hard time because of my dad.
So when I say people do crazy stuff when they are jealous and feel threatened, I'm saying it with personal experience.
