Curb the flippers part.
If individual sales were 1200 and vendors bought 300 extras there is going to be a mad frenzy when extras go live and things are going to sell out in seconds keeping aftermarket prices high and flippers doing well. If vendors bought 5000 extras it's going to be a whole lot easier to get a set driving down aftermarket prices, making it harder for flippers to mark them up enormously. If their bottom line is being pushed down significantly (on top of that Paypal fees) and having money tied up for 1.5 years there is going to be less incentive to buy things to flip, hence curb flippers.
Hypothetical example - you bought a set for $120 (then $10 shipping) and there were so many extras available that this is now worth ~ $150 aftermarket, after Paypal fees you take in $145. Was having your money tied up for 1.5 years worth that $15?
Most sensible people would say no, but I suppose there will always be that person that gets excited about even making a buck or two off something and sees their time as worthless.
