According to USATF, this is why Marijuana meets the criteria
Pure bullsh*t
Slower reaction times and poor decision making is performance enhancing?
The affects of THC varies person to person. Some people claim that it increases their focus for example. But the potential positive effects are limited such psychoactive symptoms. If we're going to ban it for simply being psychoactive than caffeine should be banned as well...
This simply reflects an outdated set of values that are not based in reality. Marijuana is about as harmless as any drug can be. It is literally impossible to consume enough to kill you. Even caffeine isn't so ridiculously harmless.
Unfortunately I doubt WADA will change there stance on marijuana since many countries, even the US Federal government officially, still consider it a dangerous substance despite all evidence to the contrary.