Bird-lovers have pushed an anti-lead agenda (for hunting) for decades and have been highly successful. They continue to make inroads into banning use of lead entirely:
"Bald eagles across the United States are dying from lead poisoning":
I think most of this is anti-gun lobbying. When people are reduced to stoning wild ducks and spearing deer then anti-gunners will ask Congress to ban sticks and stones.
...says somebody who doesn't shoot. Its a big deal. Steel shot isn't just about being a different metal. Its about a quarter of the specific gravity. A quarter of the momentum.
You shoot steel from the same barrel as lead, it's a quite different effect. Range, drop, spread are all different, and lesser.