Well some of the career earning have been turned into credits.
For example I won a 9 hole single play and received several hundred credits. I finished 2nd in 9 hole unlimited and received a few credits. I qualified for the US and British Open last year and received a couple of hats and a USGA membership.
All those items show up in my career earnings. The value of the hats and USGA membership is converted into career earnings but not credits. As TLD said other winnings in the form of prizes that are non cash show up as career earnings but not as credits in your account.