To answer your questions:

1, because under the colonial-imperial "international rules based order," might equals right.

2, because the US is a settler colonial project just like Israel. The US leadership doesn't have any problem at all with the treatment of Palestinians. They just want to maintain their "landed aircraft carrier in the middle east" and making some money off it's natural resources in the process is a nice bonus.

The US also pretends it never violated the rights of the multitude of groups it's either nearly eradicated or severely oppressed (Indigenous, Black, and Chinese, just to name a few from the 19th century).