That's the big problem with online discounters, which just about every online bike shop in Aus is nowadays. They have to keep prices low to compete with OS sites (or, had to in the past before the Geoblocks), but that leaves them with very low margins to sell.
Low margins are fine when you're selling volume, but means that you can't really discount any further without not being able to pay your suppliers, staff and other costs. Hence the "raise price to discount" structure that happens on sitewide sales. Raise all prices by 10% at a minimum, then the 15% discount won't be losing money. But if you're already low on the GP stakes, a further 15% means there's no point if you actually want to stay in the black.
Being in the enthusiast Outdoor space, I see it all too often. New businesses who literally start life as a discounter, suddenly realising they have to close shop as they're not making enough money to keep things running;