Compare to an extreme example of a market selling one watermelon for 5 dollars, and 5 watermelons for 15. Sure, the latter is a better deal, but I definitely have no use for more than one melon, and the arbitrage opportunity is not worth my time. In the same sense, I and many others do not need more than 1 deodorant at a time and I would rather save my space.

Watermelons are perishable, so that's apples to eggs.

Do you live in a microhome? Deodorant sticks are tiny, surely you can store 3 of them under your sink for months without too much suffering.

Deodorant has a shelf life. If you stock too many, some go bad before you get to use them.

Do you know what that is? I typically buy 4-5 sticks at a time when my local pharmacy has a sale on the one I like, so I buy deodorant like once a year.

Never noticed any problems with them.

> Do you know what that is

Mine is 2 years

But you still need to store all four sticks in the meantime. Some people have extremely limited storage space.