If - to take a convenient example - I use a library sorting function instead of writing my own sorting code, it's true that I haven't removed the complexity of the work my program is doing: It sorts. But I have arguably reduced the complexity of my code.

Similarly, if I factor out some well-named function instead of repeating the same sequence actions in multiple places - the work to be done is just as complex, and I haven't even removed the complexity from my code, but - I have traded the complexity of N different pieces of code for 1 such piece plus N function calls. Granted, that tradeoff isn't always the right thing to do, but one could still claim that, often, that _does_ reduce the complexity of the code.