Apparently, lead bullets don’t just contaminate the animal that was shot. If the animal escapes after being shot, it could enter the food chain and affect other animals when they consume it. Additionally, there are animals that mistake spent lead bullets (that never made its mark) for food and end up consuming the lead bullet, thereby becoming contaminated. (Source)
As of 2023, lead bullets were banned in certain national wildlife areas. (Source)
However, the National Rifle Association (NRA) is actively opposing this ban. A quick search for “lead bullet ban” will provide an overview of their arguments. I prefer not to provide a link to their website to avoid inadvertently boosting their traffic. Essentially, their argument, as I understand it, is rooted in socioeconomic factors. Lead bullets and fishing weights are inexpensive, making them accessible to individuals with limited financial resources. They also deny the current scientific evidence supporting the ban. But, the research shared by OP should help build facts against their denial.