People suggest this fairly often but it's not that simple. Buying in any quantity heavily favors buyers while hurting sellers. A random person selling a random item they got from a quick venture may not be affected, but the actual material suppliers sell things in specific quantities for a reason, and they don't want to be stuck with extra items any more than you do.

Just look at the real world. If I walk into a store I can buy a single candy bar, or a big bag of 30 candy bars, but I can't say "well I only want 10" and rip open the bag to take only what I want. I'll get kicked out of the store if I do that. The store and the candy company clearly wanted to sell things in those specific quantities. You may not like it, but that's not the store's problem.