It’s money. The answer is money. Somebody makes money by producing lead-infused products, so they pay off lawmakers to add a loophole that allows them to continue making money.
Yet people still maintain the popular fiction that corruption isn't that common in the large western countries, and that it's somehow more prevalent in the east. It's nonsense.
Everywhere there are large governments, there is huge corruption that is literally killing people so that others may be enriched without working as much.
Corruption exists everywhere, but in western countries is a lot less likely that you'll be bribing police, school teachers, medical services, banks etc as an 'individual' to get the services you expect from them. Can you find examples of people bribing those in those positions? Sure, it can and does happen. And on the whole, it's the exception rather than the rule.
And definitely not at the scale of other countries.
Big business interests affecting policy for the point of profit is a universal issue though.
Everywhere there are large governments, there is huge corruption that is literally killing people so that others may be enriched without working as much.