In the WaniKani system kanji are constructed from radicals. Therefore if something that you learned as standalone kanji later on appears as part of another kanji, it needs to become known as radical before it can be part of that new kanji. That’s mainly because those radicals each have a unique name that is being used in the mnemonics.
It feels a bit redundant but at least it’s a review that comes for free
To add on, in the later levels they could just use the radicals they used to teach you the kanji 章. But if that kanji is itself used as a building block for other kanji often enough, it’s gonna be a lot easier to just remember 章 as one unit. Reduces the amount of radicals they have to incorporate into the mnemonic (and if you’re lucky, gets closer to the actual themes of the more complex kanji). And ideally by that point, you’re pretty comfortable with 章 as a whole anyway.