They were also pretty ineffective. See that little AT grenade, fat chance of it taking out a Sherman, maybe lucky and get a half track with it (inside the half track that is) or inside a tank destroyer, but not much else. Quite a few have surfaced in the Bulge area recently, but this doesnt mean much, as the ones found could be duds (see why they didnt use them) or could have been a rear supply area. The US used them quite a bit more for anti personell, as the bazooka was far greater at the AT role than the rifle grenade
Grenades launcher from rifles were, I think, never used for taking out armored tanks, only anto personell like a tankcrew sitting on a tank or a half track full of soldiers.
By June of '44, the Germans had the RPzB-54 "Panzerschrek" launcher and Panzerfaust disposable launchers in fairly wide distribution. Since they worked wonders against allied tanks, it's no wonder the rifle grenades fell out of favor.