If you make something which significant elements of the population want illegal, you create a demand. The more you try to restrict supply the higher the 'street' price will be as supply does not meet demand.
You would think the basics of any market would be understood - but apparently not by politicians who have never done anything other than graze from the public purse.
Given a high enough ratio between cost, reward and risk many people will take a chance. Buying large quantities of drugs attracts attention from anyone 'in the industry'. If you are not an established 'player' then shopping them achieves a variety of rewards - removes competition, allows a positive relationship with law enforcement authorities, makes them look good (win - win).
All you can say is this guy was probably not the sharpest tool in the box!