Lead-free primers are a thing. The US military prefers to minimize lead wherever reasonably feasible, because the VA is expensive, and when they have to pay to clean up their ranges during routine maintenance, extremely high amounts of lead dramatically increases the price of this scheduled maintenance.

Their primary objective is still to close with and destroy the enemy, so if they still need to use lead or uranium to get the job done, the mission comes first. But if they can save money by using lead-free training ammo, that's more money they can spend on training the troops and ammo for them to practice with. And more money to issue everybody a bazooka of some flavor or another, as Ukraine is demonstrating is a really useful idea right about now.

Remember: Amateurs study tactics. Professionals study logistics!