It sounds to me like you're looking a gift horse in the mouth. Wouldn't it be better to ask, "Why does the better Scott National supplement on higher quality, larger paper only cost as much as the obviously cheaper Minuteman supplements?" And this way you'll feel better, too.

The answer to the question about pricing is to consider standard business practices. Within a certain range of quality, almost all album supplements cost about the same price to manufacture and sell. That price depends a lot more on the seller's costs for advertising, storage and shipping than on paper or printing costs. Those matter, too, and higher grade paper may cost a little more, but at a certain price point all supplements are going to cost about the same because the real costs of the supplement are the cost paid to the printer -- and that's the same for nearly all supplements, no matter how good or poor the overall quality is -- and the cost of storing the product, advertising the product, shipping it and so on. So sellers can sell either mediocre looking or excellent looking supplements on different kinds of paper for about the same price because they both cost about the same to produce and sell.
I used to gasp at the annual prices of the now defunct White Ace album supplements. But that's what they could get for them, I suppose, and I'm sure they had no trouble selling fewer supplements at higher prices than Scott does. Scott prefers to sell more supplements at lower prices. Good for them.
If you really want a heart attack, look at the prices of annual album supplements by Lighthouse, Schaubek, and other high-end album manufacturers. Their astonishingly high prices make a $20 supplement look dirt cheap. Is their paper more expensive? I don't think so. Are their costs of advertising, storing, and selling higher? Probably not. They charge more because collectors will pay more.
Compared to half a dozen other competing album makers (Davo, LH, Schaubek, etc), Scott albums are remarkably cheap for what they are. One of these other publishers' albums covering the entire stamp history of a major European country like France, Switzerland, or Germany sells for between $1000 and $2000 from LH, Schaubek, or Davo. Scott sells a similar album including all the same stamps printed on excellent paper and nicely laid out for one quarter or less of that price. It's like buying a perfectly good car for a fraction of what other cars cost. Who would complain about a brand new, well made, nice looking $7000 car?