Obsolete Space Shuttle

Why is the space shuttle, all of a sudden, after so many successful flights,
suddenly unfit for service ?

Is it obsolete, un-economical, or just plain neglected like many of our senior citizens ?
If so, why is NASA risking seven lives on it ?

I find it very hard to swallow that NASA can't see well past its own nose.
I'd expect that from Bush, but not from NASA.

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Society for the Separation of Bush and State