The small ticket items are the items that are used on a daily basis. People purchase these items all the time, especially if they have families. For example, coupons are very common of food products. People eat food every day so it constantly needs to be replaced.
Another reason that coupons are less common on big ticket items is because people usually do not purchase big ticket items all the time. When they purchase a big ticket item such as a refrigerator, it is going to last for years. It will not need to be replaced for a very long time. Usually these larger items do not have coupons but just go sale.