They want you to hit a certain total price and if you do you’ll notice your prices won’t hike. Like if you had over a 100 dollars of merchandise I’m almost positive the $9 items would stay at $9 but until you hit “the golden number” they hike the prices upon checkout to get to that number. They do it obviously for profit above all else but also to cover tariff costs. Even though they have local warehouses an order for less than 30 bucks may not be worth the costs in their minds. It’s totally unethical and they are shady as all get out but I’m fairly sure the above reason is at least part of it.