Why is a flight not made of black box if FDR can withstand high impact?

The data recorded by the FDR is used for accident investigation, as well as for analyzing air safety issues, material degradation and engine performance.Due to this these devices are carefully engineered and stoutly constructed to withstand the force of a high speed impact and the heat of an intense fire. so, my... show more The data recorded by the FDR is used for accident investigation, as well as for analyzing air safety issues, material degradation and engine performance.Due to this these devices are carefully engineered and stoutly constructed to withstand the force of a high speed impact and the heat of an intense fire. so, my question is if it can withstand these why is a flight not made of black box to prevent great damage during accidents ??? Justify me .No silly answers.
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