JCJP is now, and will continue to be free. However, it takes time, money and resources to run JCJP, such as to pay for hosting server, as well as to offer better learning experience.
JCJP collects your learning statistics information for personalized learning to improve your learning experience. However, due to computer resources limitations, not all of them can be processed and shown to you for now. It takes considerably expensive computer resources to process those statistical information and output them into a web page.
Not only to process your personalized statistics, JCJP is also eager to implement new useful features. JCJP requires better computer resources (server) to implement those features.
JCJP believes that by affording more powerful computer resources, JCJP would be able to offer more useful features and more personalized learning.
Also not to forget, JCJP would also like to offer better speed and performance of the site to improve your learning experience.