Example: You buy a Community Box, you open the Community Box. You've paid real money in order to open this box.
Expectaction: The items you've paid real money for are yours to keep forever.
Reality: There is a small chance that the item you paid real money for is yours to keep forever, and instead you are given the item on loan for 2 weeks.
This isn't explained clearly to users in the information before buying the product, and while I understand rotating items to keep the money coming in I'd rather spend more unlocking other skins in a permament box than to get an item on loan I didn't know wasn't permanent and never buy a microtransaction again.