This has always been their policy, though (wiki b/c lazy). The previous time they were power, they cracked down on opium, just like this time.

It makes even more sense now as well, as the drug cartels/warlords were basically running the show during the US occupation (wherever the US goes, organized crime and particularly drug cartels are among their first allies). The poppy production directly contributes to the destabilizing forces within the country, and the US has used such interests (along with Islamists like the Taliban) to overthrow Afghanistan's government more than once (socialist Afghanistan, former Taliban rule) at this point.