Here are five reasons.
1. Easy to get to the product you want to buy,
2. Easy to get all information you want to see before making the purchase,
3. The buy button is in a top-right prominent position,
4. The checkout process removes all menus and links to other pages.
5. The checkout next step button is always in the same top-right position.
Listen to this podcast below to learn more about how to apply this on your own website.