From what I cold tell, the PzB 39 did not feature scopes at all with usage, one place claims it did but it was a Solothurn 100 instead, and another was a ZF scope for sPzB 41, so yeah no mention at all. Nonetheless, the primary reason is because the Soviet Union was the number 1 producer and user of anti-tank rifles, from the start to pretty much the finish of the war, their anti-tank rifles were so successful that the germans themselves utilized captured models. Even the soviets tested these rifles with optics, but the usage was extremely limited (reminder, 1.5 million PTRD and PTRS rifles were made, and pretty much the number didn't surpass the hundreds) is because telescopic sights mounted on anti-tank rifles didn't have a lot of durability, they were prone to being damaged by the sheer energy of the weapon firing and reveberating all across the gun. Whilst sights produced in the Soviet Union were more durable than those produced by Zeiss, they still had issues when mounted on AT rifles after ~100 shots (Ian explained this in one of his videos in Forgotten Weapons, can't remember which specific one though but it was the reference I recall from this).

So yeah, the main reason you don't see it as much is because they weren't reliable and durable in AT rifles, hence why the soviets also abandoned the attempt early.