1) The stuff works.
2) There's already a refined clinical version of it in the works.
The cynical part of me also assumes that the clinical version will take the harmless natural version and refine it into a super addictive monster that will reliably kill elephants when slightly mis-dosed. Everyone will then abuse this as usual.
Fast forward 20 years and shady chemists learn that it's possible to take the structure of cathinone (as a basis), tweak it here and there, and come up with purified "substituted cathinones". AKA: "bath salts" (MDPV), mephedrone, methylone, and countless others. Some of these were frankly nasty.
Today, the US decides to ban kratom, which has been naturally used for recreational purposes in Thailand and elsewhere in Southeast Asia for centuries.
I wonder if substituted mitragynines are in the future. Very possibly. If not from the pharmaceutical companies then from future sellers of "bath salt" type substances.
Either way, there's something very culturally insensitive about these type of bans, in my opinion -- these laws carry a whiff of "these are drugs that these other people do". In today's drug enforcement culture, apparently the khat cafe is horrible, but the pub and the coffee shop are a-okay. Personally it's hard for me to see what the difference is between the two, except the pub / coffee shop are accepted by well-off Western Europeans, and the khat cafe is mainly populated by poor Somali / Yemen / etc. immigrants.
Technically, barring any sort of breeding modification I doubt was done, those Catha Edulis plants in the US botanical gardens are quite illegal, being a "material" that contains cathinone.
Now, in practice, of course, no one is going arrest the Architect of the Capitol for growing Schedule I plants on their property for ornamental reasons. Heck, San Pedro cactii already set a murky, not-quite-defined precedent for this (https://erowid.org/plants/cacti/cacti_law1.shtml).
Then again, despite the relative obscurity of khat, there have been a few cases where people have been arrested for cultivating the plants. Such as this case here in 1998 -- http://www.sfgate.com/news/article/Prunedale-Man-Charged-in-...
Of course, in that case, the arrestee's name was Musa Ahmed Gelan, not Stephen T. Ayers. So it goes.
Edit: But looking at the side effects http://www.narconon.org/drug-abuse/kratom-effects.html - if any of that's true I guess DEA may be right in making in a controlled substance to save people the misery or possible death if nothing else.