Before the US left the WHO, EU institutions and countries contributed around 57% of the costs. So almost three times as much as the US, despite having less wealth (79 trillion vs185 trillion), and more citizens (452 million, 320 million in the USA). Poor countries aren't expected to contribute. Obvious, I would have thought.
And yes, it's not only about charity, but the people whose lives are save by aid really don't care.
Besides, you may regret the soft power you've lost, as China moves in and takes over.