I know "super-earths" are quite common in other planetary systems, but there are none in the Solar System. Is it due to the material that could have created a single large super-earth being used to create four smaller terrestrial planets in the Solar System?
I think the answer to your question lies with Jupiter, be it directly or indirectly, the gas giant is now believed to have had a large influence on the way the inner planets formed.
Many planetary scientists believe that the reason we only have 4 small inner planets today and not any "super-Earth" sized ones is because of Jupiter, and how it interacted with the circumstellar disk and protoplanets at the time of the solar system formation. There may well have been one or two super-Earths that formed in the early solar system, but models suggest that they would have been sent crashing into the Sun by the inward advances of Jupiter.
I found this blog article which explains it in more detail. And there is also another MNRAS article that goes into more detail about the physics and orbital mechanics behind what might have happened in the early solar system.