Scarcity is a form of propaganda, a way The Party gets the proles to jump on the bandwagon. It's a way to manage suffering, to dole out poverty, to build false patriotism: "The Party needs razor blades for the war effort. You would rather it go to the front lines than to you, the spoiled public, safe at home, right? Support your country. Do without razor blades!"
It's a means of control: supply and demand. Like the war with Eurasia. Or is it Eastasia? Is there a shortage of butter or razor blades this week? What's the price of chocolate? Keep the public guessing and uninformed and no one complains. Always changing the price gives it a kind of legitimacy, as if market forces are really at work. But it's all a ruse, really.
It's like the shortages at the gas pumps and the price of gas during a war or a recession. It's a way to make headlines by the Ministry of Truth. It's a way to keep the masses from rebelling by the Ministry of Plenty. Keep them hungry, but not too hungry. Take away razor blades, but not for too long. It's revolving door propaganda: flavor of the week bandwagoning.
It's also a satire of the USSR's many "Five Year Plans." The USSR was famous for its scarcity during the Cold War. One year the whole country went without toilet paper, I think. But there were always enough fighter planes and ICBMs to keep up the Americans.