Sterility is the enemy. Folks soak in H2O2 to remove pathogens from the seed hull, but a sterile environment means that the first organism to get a foothold (often molds) dominates the environment.
My beans are intentionally caked with beneficial bacteria, and watered in with 24 hour porch fermented potato water.
Also, for more context, check out
A popular and widely used germination resource here on Overgrow!