Tell me how this 27 year old maf still works while the new one doesn't.
Because the signal from the LS1 maf goes through the Gen2 translator which modifies the signal so that 1) it's compatible with the GN maf and 2) to affect some tuning of the car.
From the Gen2 Manual:
The primary function of the MAF Translator Gen-II is to allow the user to
adjust the air-fuel ratio of their engine. This is accomplished by adjusting
the amount of airflow the Engine Computer Module (ECM) or Engine
Control Unit (ECU) perceives is entering the engine. If the ECM/ECU
senses less airflow is entering the engine, it will command less fuel be
injected into the engine, thus making the Air/Fuel ratio "leaner". If the
airflow signal is reduced by 1%, the resultant fuel delivery will be less by
1%. For example, an engine is consuming 100 grams of air per second, and
the ECU is delivering fuel for 12:1 Air/Fuel Ratio (AFR). If the airflow
signal to the ECU is reduced to 95 grams per second (-5%), the ECU will
delivery fuel for this amount of air. The resulting AFR will be 12.6:1 (5%
leaner).