If language came about because people formed committees to invent each
language, they probably would do it differently, and they probably
would not give multiple meanings to a single word, but that's not, of
course, the way languages come to exist.
Languages have different meanings for a single word as a result of the accidents of history.
Sometimes two words sound very similar. Over the years, people start to pronounce them the same. For example,
shock as used in
a shock of grain comes from the Old Saxon word
scok, and
shock as used in
shocking behavior comes from the French word
choque.
Sometimes two concepts are similar enough that it makes sense to use the same word for both concepts. For example,
safe means secure from danger, so a strong box where you can feel secure storing your money is called
a safe.
People get used to the the idea that the same word can have multiple
meanings as languages change over time. Each word which has
multiple meanings has its own history and some unique reason that
applies only to that one word. There is no general answer that
applies to all such words.
CJ