It's a puzzle
There's a theoretical and observational gap when micron-scale dust is forming into 1 km wide planetesimals - between the two sizes, gas drag does weird things, like spiralling boulders into the Sun. Just how to get from a-to-b has yet to be determined. If terrestrials are rare then perhaps there is no path from dust to flying mountains and the big planets or their cores form via gravitational instability or something similar. And terrestrials might then form from the cores and debris after collisions have stripped off the outer layers of gas giants. Earth and Venus might be such core remnants, while the others, including Theia/Luna, are former moons.