Also slang terms are popular for a short time, and these are hard to be understood by outsiders. This changeable characteristic does not fit with universal usage. The world data have to be fixed all the time, and future people have to learn too many words. This system supports an unstable world. But people seemed not to like speaking tight.
Vocal languages have to be natural for people's feeling.
Even a Japanese person can get the same meanings through the characters with their own vocal language without feeling like they are a foreign language, since their ancestors adapted them around the 6-7th century. As long as you are using only an alphabet language, you can hardly understand the rationality of this Hieroglyphic type of characters. Alphabets evolved through Hieroglyphs a long time ago, so you might think that the Hieroglyph is a past, old, and a inferior system. But actually as a universal language, it has worked much more rationally than Latin, Greek and Sanskrit which have been used for universal usage by only specialists with much effort. China has governed their big country using the same symbolic characters beyond cultures and time.