Experiences like this have taught me to be careful about over optimizing. If I want one of something, and can't use (or don't want to use) more than one, it doesn't matter if buying two (or more) costs less than buying one; I should just buy one.
Bulk-buying mentality is so prevalent in the US, it can sometimes be hard to avoid, and I think US urban planning has a lot to do with it as well - e.g. in many cities I've lived in the US, it would take longer to walk to my car than to walk to a grocery store when I was living outside the US, so you get trained to focus on economizing trips.
My wife and I both favor bulk shopping for a majority of our household goods, and when we pondered why, it came down to our families having done the same and followed that thread to our grand/great-grand parents that lived through the great depression.
Having bulk food/household goods means that at any point, if income halts for any reason, we still have X number of meals/tp rolls/litter changes before we enter the danger zone. That was reassuring when we were living paycheck to paycheck.
I do agree on urban planning being a part of it as well. It's a 15min drive to my closest grocery store, and 10 minutes of that is driving out of my neighborhood. Walking to the store is nearly impractical, and generally not safe due to the lack of sidewalks for a fair stretch of the main road.
I have friends that "need" big SUVs if only for their Costco/Sam's Club trips. Whose homes by square foot would be palatial mansions and palaces to royalty of many previous generations, but are cookie-cutter one of hundreds in over-vast neighborhoods full of them, with rooms dedicated to bulk goods storage. It's a fascinating world.