Just like lead shot, it is about lead toxicity in wildlife, especially in raptors, and raptors are federally protected. All of the caterwauling over lead shot beginning 35+ years ago, will again be heard if or when lead core bullets are prohibited. The USF&W service proposed in 2017 to prohibit lead core bullets on federal Wildlife Refuges, but nothing came of that this time around. One of the upper midwest states proposed a prohibition, I don't know what has come of it.
I don't like it, but there are legit reasons behind it.
Raptors won't be affected by .22s because .22s don't do this.