Amazon gives non-Prime members free shipping at $35 or more of eligible items. Instead of simply letting users get the product with free shipping, they’ve added a discount that prices it exactly one cent below the $35 limit, while only subsidizing the price with $3.38, which is about half of what they’ll then charge you for shipping.
Because you already have an account set up with amazon.
Because you’ve used amazon before and feel comfortable with them.
Its just not a business I would recommend giving your money too, but its your choice.