The US organizes its foreign policy around domination and scapegoats. China is a natural target due to a confluence of several contradictions of capitalism (and by extension, imperialism). You’ve asked the right question, though: why now?

Personally, I believe we’ve simply reached the tipping point for China’s material prosperity to threaten Americans’ sense of superiority as well as America’s ability to maintain a unipolar world order - or at least, this is what the monsters involved in US foreign policy believe. I don’t think your average American thinks Chinese people have good lives, but they’re constantly being exposed to contradictions of the idea that it’s an impoverished backwater. In addition, China is not subservient to the unipolar neoliberal world order. This is, as it always has been, interpreted as a threat to the USA itself and their idea of combating it is to villify and apply negative pressure on any country that will “listen”.

Also, The War on Terror has reached its end of life in the public consciousness.

So the US has been leaning on its propaganda arms to push all kinds of anti-China narratives in a kind of “see what sticks” approach. The hope is surely to drive negative public sentiment so that sanctions and other attempts to isolate China (the only thing these monsters know how to do) will be accepted.