14 days ago
Many shop owners sell things for not only diamonds, but also iron and even gunpowder or other things such as slimeballs. People have their own designated shulker boxes in which they store their things in. It is just convenient when you want to buy or sell something but it's in one of your many shulker boxes that you can easily take out if you had this system instead of going back and forth.
And as Awkwardbowman said, people like to buy in bulk and if they run out of space (which is already taken up by many possible currencies, tools, and food) they may stop shopping altogether if their inventory space has run out or they would have to spend more on eyes. Also I think many people are mature enough to not abuse said system.
Also I forgot to mention that landowicked has installed this system on the side of their shop, many people have benefited from, such as myself - and I sometimes just go all the way there to organise my things - if people would like to take a look.