WaniKani organize kanji according to the radicals they teach, and generally keep in the order of JLPT/frequency/strokes. It’s true that there may be some seemingly common kanji or vocab found in later levels, but there has to be a compromise between having a system and just throwing in whatever they want wherever. Also, like Leebo said, the point of kanji is to be read, and WaniKani is first and foremost a kanji learning program. The common spoken vernacular will be different from the common kanji you’ll see, if this is the metric you’re going by (i.e. 綺麗 is not taught until level 29, but you’ve probably heard きれい before. You’re also much less likely to see 綺麗 than to hear it or see it in its kana form).
Regarding the vocab: they’re there to help you remember the kanji, and sometimes that means you’ll be taught vocab you’ll barely ever use in day-to-day things, if at all. There are some funny stories related to this, with the best one being Naphthalene’s experience with 里心.