US citizens are allowed to access Chinese social media even though Chinese citizens are not allowed to access US social media because the Chinese government is oppressing their people and trying to prevent them from accessing foreign information sources, whereas the US government is not yet oppressing their people in the same manner (and constitutionally forbidden from doing so).

It sounds unfair from the perspective of companies wanting a right to market access, but companies do not have rights, people do. People's right to freely choose where they get their information from trumps companies' non-existent right to have the government shut out their competitors.