Businesses invest in product development and marketing to bring a customer to them. The customer is convinced of the value of the thing they want to buy and puts in their credit card number. Sometimes it doesn't work, for example because a poorly understood interaction of systems at their bank decides the charge is likely fraudulent. (Ask me about how a particular US bank has caught 17 of the last 0 times a fraudster in Japan used my credit card to purchase software.)

Some percentage of these customers retry, perhaps with another card, and eventually succeed in buying the thing they want to buy. Some don't, and the business loses the revenue that a customer was already happy to give them.

Improving authorization rates (the industry jargon for that) recovers that revenue, for ~free (your product/advertising/etc spend to attract the customer is the same whether they successfully complete the purchase or not).