Their trade with China maybe negligible, but they must still rely on foreign investments. China hold a lot of sway with global companies. They can choose either Chinese market or those fringe markets. Time to use that leverage. The west will scream of course, but who give a rat frack.

As for trade and investment with Taiwan, it is pretty complicated. While it benefit Tiers, I still think it also has benefitted China, not just in term of economy, but also in term of soft power. While some wan wan think they can live without China, but with more and more of them having trade relationship with China, or invested in China, or receiving investment from China or working in China, those perception will change slowly to the benefit of China. If China cut them off entirely, their economy will suffer for sure, at least in the short term. But in the longer term, their connection with China will also diminish, and if they can diversify, than it will be even worse for China. Cutting them off will only work if China also blockade the island from trading with the rest of the world.

In fact, I prefer if China add the carrots when dealing with wanwans. Make it easier for them to live, study, do businesses and work in China. Maybe give them a Mainland ID cards, after all China do consider them citizens. It is even better if they can find loves and spouses in Mainland. The more they have positive interaction with Mainlanders, the more China can attract them to the unification cause.

DPP is desperate to prevent Taiwanese from having deeper interaction with China. That's why DPP banned Chinese products and investments. Why should China help DPP by doing the same? If Chinese goods and services can't reach Taiwan, let's make it easier for Taiwanese to come to Mainland to enjoy the Chinese goods and services.