I think raising such an issue in fact makes you think what it really is that you wish to change. Is it to create new words about something, wish people thought more like you or is it that you hope you didn't have to explain anything to people.
I suppose one obvious answer to why we don't have exact words for everything is that not everyone thinks the same way and everyone uses a language in their own way. A rational way of thinking about it is that peopel are capable of combining words with other words to create meanings and explain what they want to say. Also, the diea of creating words with specific meanings naturally raises the question abotu whose meaning it actually is and who defines what meaning everyone should use. Which one group/entity is entitled to rule the meaning for a whole number of language users?
An accurate vocabulary would require that everyone thinks alike and that there is no room for adaption or changes. Therefore, if we do not have an accurate vocabulary, what does that imply?
I'm not saying what is right or wrong, however, those are just some thoughts that popped into my head about the question.