You can only use it once before it gets earth contamination. It's been 50 years an we haven't got anymore. Even though there are missions planned the might lose

You can only use it once before it gets earth contamination. It's been 50 years an we haven't got anymore. Even though there are missions planned the might lose funding or fail, so who knows when they might get more? Also, science advanced with time, if it's all used up, we wouldn't be able to use future tech to analyze it.