Why is it theorized that the asteroids did not merge to form a planet?

Asteroids are believed to have not merged into a planet due to the gravitational influence of Jupiter, which disrupted the accretion process during the early solar system's formation. This strong gravitational pull prevented smaller bodies from coalescing into a larger planet, resulting in the formation of the asteroid belt instead. Additionally, the varying sizes and orbits of asteroids contributed to their inability to collide and merge effectively.