Good for him, he is quite brave regarding how much he uncopyrighted. But still, I checked just now and - correct me if I am wrong - not all his books are free, for example "The Little Guide to Un-Procrastination". Also, he is selling courses.
As I understand it, he is selling some products, and uncopyrighted some others for marketing purposes. Interestingly, some people will pay also for those works which are uncopyrighted. Still, it isn't the case that everything he offers is free and can be paid only voluntarily.