Graham Sutherland / Polynomial@greg for the same reason, capacitor manufacturers tend to do failure analysis by physically cutting the part out of the board, rather than desoldering it. the heat would alter the lattice and mess up any measurements or crystallographic analysis they want to do.
it's also why you shouldn't run calibration on test equipment immediately after doing hot air rework. best to wait a few days for the initial rapid capacitance decline to settle down.
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