What makes sense is that the companies standardize on packaging. If most of a pill producer's output can fit reasonably in a few different sizes of container, then less time needs to be spent hunting down varied containers, ordering them, inventorying them, setting them up, allowing for them in packaging equipment, and so forth. Just stop the line, change the pills and labels and start it up again. "slack space" shouldn't be an issue to the consumer in this case - you are purchasing based on count, not on volume. The cost of packaging is minimal, and far outweighed by the other costs I mentioned. Bottom line - not an issue.