My (totally uneducated) guess is, in the early formation of a solar system the material is hot and volatile it is all moving around a lot. There are a lot of large / medium sized bodies moving around they are running into each other, joining, breaking apart, moving around, etc. In all that chaos, the available material is tossed around and "excess" material is toss out of the inner planet orbit.

I am imagining it like pouring a cup of sugar on a dinner plate and shaking the plate around until the amount of sugar on the plate is sort of stable. The excess material ends up outside the solar system (Oort cloud / kuiper belt) or part of gas giant cores and moons.

With that, there is only so much material in the inner solar system to work with and the law of averages works out and we end up with similar sized planets.

I would assert a hypothesis that a ratio of material in the inner solar system is linked, in some way, to the size of the star. That it is unlikely there will be massive earths out there in the inner solar system because of this natural distribution of material around a star.

I have no formal training at all. Just an IT nerd that watches a lot of Kurzgesagt.