After doing like two years of it in college, I can tell you that learning Japanese is kind of a nightmare after a while.
Hiragana / Katakana isn't so bad, but when you get into Kanji you're basically learning vocabulary along with symbols at the same time, and you're expected to learn a ridiculous amount of them. By the time high schoolers graduate in Japan, they know an average of about 10,000 words and symbols, some of which have several meanings, just like they do in English. Pair that with having to speak all of it fluently as well, and it kind of makes your brain melt after so long.