Because satisfied customers are loyal customers. Loyal customers come back and buy from you again, and tell their friends all about the great service they have received from you. Then their friends come and shop with you too.
Customers that are dissatisfied or just feel neutral are more likely to try the competition. They won’t tell you, they will just do it, and they may never come back to you.
Big businesses know this, and carry out customer surveys all the time. A number of small businesses however will often skip market research as they feel that they cannot afford it or that it is not relevant to them. However customer research is important regardless of business size, here’s why: