Lead-free ammo is much more expensive, and gun regulation is a politically charged topic. Any attempt to ban lead ammunition will, rightly or wrongly, be perceived as an attempt to discourage recreational shooting by making ammunition less available. Much like California's handgun drop-safety requirement is currently perceived as an attempt to discourage handgun ownership, by making them less available, or Texas' recent abortion regulations are perceived as an attempt to make abortions less available. They're ostensibly regulations enacted for health and safety, but nobody affected by them believes that story.