A larger pack is a bargain only when the unit price is lower and you can use the product before waste or spoilage.
Compare unit price
Compare cost per kilogram, liter, item or dose. Package size alone does not tell you the value.
Consider shelf life
If half the product spoils or loses effectiveness, the savings disappear. This matters for food, cosmetics and some household products.
Bulk can increase consumption
When supply feels unlimited, people may use more of the product, changing the real cost.
Check storage space
A bulk container is less attractive if it lives in the middle of the kitchen for a month. Storage space has value too.
Bottom line
Keep the solution simple: start with the most likely cause, change one factor at a time, and observe the result. That makes it much easier to identify what actually works in your situation.