frost line for solar nebula = 3.5 AU => 150 Kelvin
rock and metal can exist beyond 0.3 AU => 1300 K

Rocks + metals account for ~0.6% of the solar nebula
hydrogen compounds (water, ammonia, methane, etc.) ~1.4% of the solar nebula
hydrogen + helium ~ 98% solar nebula

After forming disk, the disk would have cooled as heat radiated to space. But before ices could clump closer to Sun than frost line, Sun turned on (started nuclear fusion) and strong winds during T-tauri stage swept out remaining gas. If the nebula had cooled more quickly, the inner planets might have been able to get bigger and have more hydrogen compounds in them. If the nebula was warmer, then the frost line would have been further out so Jupiter would have been a terrestrial planet.

Further out than Neptune, the ice cores weren't big enough to capture the hydrogen + helium gas => stayed small dwarf planets or comet nuclei.