The English language has more words in it than any other, and around twice as many as koine Greek.What would be better would be to address why more than 3 English words are used to convey essentially 2 word meanings, finish and fulfill?
Why translate the same word meaning into more than one or two English words or phrases?
Therefore, when one attempts to translate from Greek into English, one usually has a choice of which English word to use, each with a different shade of meaning. The context is what will determine choice.
While the above is true, it does not hold good for every word. There are three Greek words which can be translated as 'love:' philia, agape and eros, although the latter does not occur in the New Testament. Again, the context will help, but an authority as well-known as Don Carson tells us that philia and eros are synonyms - that there is no difference between them.