Establishing diplomatic relations with the Cook Islands and Niue are strategically considered moves in response to growing Chinese influence in the region. The goal is not necessarily to ask countries to choose between Washington and Beijing; instead, it is to help ensure a "free and open" Pacific that is peaceful and hospitable to commercial shipping, especially after China's assertiveness has forced the US to pay increased attention to the region.
The South Pacific is of strategic interest to both the United States and China. The geopolitical rivalry for influence has prompted President Biden to diplomatically sweet-talk Pacific island leaders so as to win them over in the battle for influence against China. Those leaders know this, so are now seeking US financing for climate change adaptation and infrastructure projects — the world waits to see if Biden will deliver on his promise to bring the US checkbook to the summit as Washington scrambles for influence.