The pharmaceutical cost to make this stuff in the quantities and frequency of differing dosages makes it easier and cheaper for them to package the median dosage for most patients in a vial while keeping it at 4, and they always always pack extra so nobody gets less than prescribed.
For a lot of drugs, the cost to manufacture once the research is done is higher than the cost for the bottles/prep/packaging/certification/inspection.
It's stupid but it's how they work.