The reason is, is because there are many rights.. By their very nature, they are not supposed to be able to be taken away. By writing them down, the thought was that this enumerated *all* of the rights a citizen had, which would lead to the government trying to work around them. By not writing them down, this was supposed to ensure that if a government ability wasn't enumerated, the right was reserved to the citizens.
That same conflict occured in the formation of the US of A and the signing of the Constitution. The Federals did not want them written down, because they feared that by doing so, the government would assume the non-enumerated rights and wittle away at the enumerated rights. But a comprise was made for the Constitution...and we have the Bill of Rights(a list of supposedly the most important ones).
Profact: The Constitution and then-established laws were originally a limitation on the ability of the government. The intent was to say"If it's not here, it's reserved for the States or the people". You can thank Abraham Lincoln for shitting on that idea.
