The USA - which is currently kidnapping the children of refugees and sticking them in concentration camps - has consistently complained that the UN Human Rights Council is not fit for purpose. For a start, it criticises Israeli human rights abuses - something a human rights organisation should apparently never do. But the US is also annoyed that countries which persistently abuse human rights are regularly elected to the council. So they're quitting it.
I guess they're finally admitting they're a human rights abuser, and being the change they want to see in the world.