How many irregularly spelled words do you think there are in the English language? Exceptions to phonetic pronunciation, silent letters, loan words spelled like they would be in foreign languages rather than in English, etc. In the end, these number greater than the quantity of kanji Japan possesses. But we have them all memorized. We know them all because we are exposed to our primary language every day. A person doesn't really 'study' their primary language. They learn it through immersion.
For a native, learning one kanji would be equivalent to your learning that it's receive rather than recieve (when god knows it should be neither, but reseev). This enormous amount of time you think it takes to learn kanji is founded on your ethnocentric perspective which fails to realize the ease with which one learns something through forced exposure. They will learn it without trying, even if they don't want to, just as we pick up the proper spelling of our countless English irregulars.