I think China is building military capability because they think they need it. We don’t know why. If you think about the game theoretic aspects of this, then it makes sense for the US to preemptively mass forces nearby even if they believe China’s ambitions are peaceful. You can’t just assume that because your opponent is telling you that. And vice-versa if you’re China and you see the US massing forces.
The fact that Chinese fishing ships invade other territorial waters to steal fish and damage habitat and the fact that the premier wants to bring Taiwan back suggests a will to be the aggressor.
China didn’t increase defense budget accordingly and for now still sticking to the same gdp percentage (around 1.5%) so the spiral hasn’t started yet (surprisingly).
Also China is always aggressive to DPP which isn’t something new and US government well understood the reason and used to assure China they will deter DPP’s independence agenda (if you’re familiar with that history. also https://www.foreignaffairs.com/taiwan/taiwan-china-true-sour...). Unfortunately there isn’t much political room now in US for that kind of assurance.
The fact that Chinese fishing ships invade other territorial waters to steal fish and damage habitat and the fact that the premier wants to bring Taiwan back suggests a will to be the aggressor.