Then why has Shi Zhengli continued to support the zoonotic crossover theory as the most likely when the communist party no longer does?

They left that behind a long time ago in favor of "The US did it."

Scientists in China play balancing acts all the time. They have to assess the risks and decide on a case by case basis what to say. I’m not inside her head but perhaps she also wants to try to maintain some scientific credibility for herself. It’s fine to wonder why, as you are, as long as you don’t assume that the question existing acts as a validation of your position.