It's government control for the grower's own good. The grower , under the regulations is required to test for THC. The regulations do not allow any more than a THC content of 0.3% THC .
Planting foundation , registered or certified seed will consistently produce plants with a THC content of 0.3% THC or less. A grower planting home grown seed would , if the THC tested over 0.3% , be ordered to destroy the crop.
btw, the government is not in the business of selling seed. They establish the standards and ensure they are maintained, nothing more