The most compelling explanation for US soft power is balance of threat theory[0]. Soft power comes from you not being seen as a threat, and you being seen as a way to prevent other threats. Because above all, countries prioritize security.

The status quo in US foreign policy was that as long as you're pliable to US interests, then the US was nice to you. You get democracy and get bounded autonomy, more autonomy than was afforded to subjects under any previous empire, to the extent that people would question whether the US even was an empire. Despite US being incredibly powerful militarily, the US was seen as non-threatening to friendly countries. That was an incredible magic trick, since those two things are usually correlated. This drew countries into its orbit and expanded its influence.

Countries could see the contrast to being in the Soviet Union's orbit and having your grain stolen, your people getting kicked out (Crimea) or being put into a camp.

This theory is a way to conceptualize the problem with Trump's bellicose and volatile attitudes towards Canada and European countries. If everyone sees you as a threat, this theory predicts that they will balance against you. In concrete terms, this theory predicts that countries who aren't threatened by China (due to being far away) will become closer to China if they feel threatened by the US.

[0] https://en.wikipedia.org/wiki/Balance_of_threat