Ahh I see sorry I thought you were a new customer.
Yeah they can be annoying. Mobile is a challenge because you can’t really do a pop up that’s not hugely intrusive because of screen real estate.
My guess is they’ve A/B tested it and having the pop-up is a high enough conversion they just leave it on.
A better way would be to just have that gift icon shake encouraging users to click it and put the discount info on there.
The Shopify thing is probably handled by the Shopify settings. These days it’s just way easier to plug Shopify in for commerce than build something proprietary. As a result there’s a lot of ‘out the box settings’ that can make checkout processes annoying if not tailored by the company using it.