Because each method has its pros and cons. It's a difference of generality and specificity. Consider this list as a ranking: 0 and 1 >> alphabet >> Chinese >>

Because each method has its pros and cons. It's a difference of generality and specificity. Consider this list as a ranking: 0 and 1 >> alphabet >> Chinese >> picture. All 4 methods can be useful in some cases. Chinese has tens of thousands of characters, some people consider the language close to pictures, but real pictures have more than that （infinite variants). Chinese is harder to parse than alphabet, and picture is harder than Chinese. (Imagine a compiler than can understand arbitrary picture!)