Because these failings, if you really think so (what was problem with 37mm HE round?) were insignicant compared to the importance of the defective 76mm AP and HE shells. Really, how one can say the importance of a 5 rounds of special (perhaps somewhat naive designed) rifle ammo issued to German infantry, that would be used against occasional armored cars etc. equals the importance that US Tank Destroyers simply couldnt do their job proper against common enemy heavy tanks (Panther, Tiger)...?