Because "flowers" (the dense little resin-covered nuggets you buy when you buy pot) are a small part of the pot plant. The rest of it contains some THC, but is

Because "flowers" (the dense little resin-covered nuggets you buy when you buy pot) are a small part of the pot plant. The rest of it contains some THC, but is not suitable for selling to smokers. If it weren't used to make THC oil it would be thrown away.