There is a difference between lynching and hanging.
Lynching is hanging by a mob without a trial and verdict. That’s already illegal. So I’m not quite certain what the new law is all about.
The new law makes it a federal crime. It was needed in the 20s-50s in the south, because democrats didn’t enforce laws against murder very well when it was a black victim. Democrats like Fullbright and Byrd filibustered it. It’s not needed any more, but democrats want to federalize everything, so they are for it now.