RPG-7 entered service before the PzF44 and is a development from the RPG-2, which was pretty much a combination of the Bazooka and the Panzerfaust 150. Firing a rocket out of a tube is pretty much the simplest weapon you can build so of course they all are going to look and work very similar. And having the rocket in the front allows you to have a bigger warhead without needing a bigger and heavier tube.