This is absolutely preposterous.

There're a few possible ways to interpret it... I want to consume GABA and die off in the process, why would someone care.

1. The agencies are being benevolent, caring for the society's health, in the process aiding in reducing public healthcare expenditure and an alleviating an overly congested public healthcare system.

2. Or you're afraid that those having superior knowledge, access to, and $ to buy performance enhancing supplements will be a threat to the rest of the population.

3. Purely monetary reasons, including taxation, and benefiting a few well-connected corporations.

Yet when someone dies consuming unlicensed products, everybody will blame the govt for not taking action. 

I guess a better way could be to issue public health warnings instead? 

Unless it's proven to be a health hazard, then by all means ban it.