However, consider a senior developer. He's a master at programming, so actually creating new code would only take one working memory slot. He's familiar with the syntax, reserved words, data structures, if statements, everything. It's as second nature to him as eating. Therefore, he now has 3 other working memory slots as opposed to our novice programmer whom occupies all of them because he hasn't completely chunked the skill of programming yet.
It's similar to DNA. The DNA molecules are so incredibly long and complex, that in order for the cell to accommodate it, it has to be compressed by being tightly coiled. This is similar to what happens to complex ideas when they are chunked. They're more able to fit inside our working memory.