It's easy to not appreciate this, but in a way the hardest thing about learning a language is mastering the vocabulary. Think about your native language. When was he last time you encountered a grammatical structure you were unfamiliar with? Now when was the last time you encountered a word you were unfamiliar with?
If you're studying two related languages, like Spanish and English, you get a huge boost from the fact that the more difficult words are actually more likely to be the same. You don't have to study very hard to understand what "planeta" or "geografía" or "farmacia" mean. On the other hand, if you're studying Japanese, you have to memorize words like "wakusei," "chiri", and "yakkyoku" which have no resemblance whatever to the English words. And it just goes on and on and you are never really done encountering all the words you will ever encounter. Compared to this slog, mastering a grammar and the number of irregularities typical of a natural language is a minor annoyance.
The script is not really an issue; Chinese is the only major east Asian language (or language family) written exclusively in Chinese characters without a phonetic script, and even then the Roman alphabet is familiar.