A lot of tickets were sold online or on the phone and charged to a credit card. The actual credit was never presented. Like you said, an ID is relatively easy to fake so Airlines check CC to reduce their loss.

I am not encouraging any fraudulent activity but let me give you an example. Some one can steal a credit card number (eg, from sales slip) and use that to purchase ticket for the upcoming weekend for a quick trip. It's relative easy to fake an ID for check in. In fact, there is really no need as that person can use his real identity but with a slight variation of first name. Instead of William J. Smith, he can buy it as Bill Smith or J. Smith... he will have the right ID to board.

By the time this charge is discovered... usually weeks later, the trip is long completed. Yes you will get a name but would that help to track down the thief? Where are you going to find J. Smith as there are thousands in USA?

This happens frequently so airlines decided to stop their loss in revenue by seeing the actual card.