The DEA has placed a temporary ban on Kratom, making it a schedule 1 drug under the CSA.
If you want to understand the motive behind FDA and DEA policies, you shouldn't ask what is the morally correct thing to do, but rather what will be the most profitable for the pharmaceutical industry. The morally correct thing to do is to allow individuals exclusive control over what they put in their own bodies i.e. to not breach self-ownership. However, this is not the most profitable thing to do since medicinal herbs like kratom cannot be patented and sold at exorbitant prices like Oxycontin and other prescription opioids which, unlike kratom, claim thousands of lives per year. We must also be mindful of the private prison industry's cut of the fleecing; their bottom line matters too. With violent crime rates at a 50 year low, the government must criminalize more victimless activities to ensure that they meet lockup quotas, or else the private corrections corporations might sue them for breach of contract. And if you take a careful look at other industries and trades, you'll notice that a pattern will emerge that is not merely an accident, but is there by design. The neoliberal system does not operate for the benefit of common people, but rather the political class at the expense of the common people.