Because the government can't turn around and unilaterally ban something instantly. This is a good thing. Building a body of research evidence, drafting legisla

Because the government can't turn around and unilaterally ban something instantly. This is a good thing. Building a body of research evidence, drafting legislation, putting it out for review, getting it passed into law, etc. all these things take time. It could then get challenged legally which would obviously take more time. Plus you then have to give companies time to figure out what's in their pipeline and remove it. The legislative route could easily take years longer than companies willingly switching away based upon preliminary evidence. It took a decade for DDT to be banned and that was with a lot more evidence against it.