In the nebular hypothesis, why did the nebula start to collapse?

Although I'm not an expert, I seem to recall reading that solar systems often begin with clouds of unorganized matter measuring 20 parsecs (65 light years) across. Most of them are hydrogen molecules. The pressure required to hold the molecules together increases with temperature, but because the typical temperature is around 12 k, the pressure is negligible. It originates from the gravity of the cloud itself. Material from novas, colliding neutron stars, and high-speed material jets emerging from stars and black holes all contribute to the continuous enrichment of such clouds. That adds those heavy elements—like gold—that can only be produced by the rapid neutron capture (rNC) process as opposed to the simple nuclear fusion process (slow neutron capture). These clouds spontaneously emerge from floating pieces of material, hold together for millions of years, and eventually disperse. A component of the cloud condenses along the route for a variety of causes, including localized concentrations of greater density or shock waves from supernovae. Unbalances in the cloud lead it to split up when condensation takes place. Then those fragments shatter once again, leaving you with barely enough for a solar system. It would have been within 3.5 light years of the initial cloud for our galaxy. The contraction up to this point has been isothermal, which means that heat is being radiated so quickly that temperature stays mostly unchanged. The creation of a Bonnor-Ebert sphere comes next. Although such zones frequently appear in photographs in a faint manner, this is only a hypothetical area in which there is a certain amount of mass. The First Hydrostatic Core is located here (FHSC or First Core). The First Core can be imagined as a pre-proto Sun with an interior temperature of roughly 300 k and a radius of 1 AU (the same as the Earth's orbit) (26.85 C or 80.33 F). Although it first begins off chilly, it ultimately warms up to 300 k and then grows even hotter over the course of years. The friction of falling materials and adiabatic contraction provide the heat (the kind that makes things hotter). Hydrogen molecules start to break down into atomic hydrogen, which is more dense and falls to the center, at temperatures between 1500 k and 2000 k, on average. Eventually, the atomic hydrogen coalesces into a protostar-sized Second Core. Because the entire system is rotating swiftly and because momentum is being lost in some areas owing to gas shooting off, an accretion disk has already formed. Although in our instance it would have also been a protoplanetary disk, the disk is a protostellar disk. The protostar is regarded as a star until it becomes hot and brilliant enough to begin ejecting the gas and dust. (Prior to it, infalling gas and dust are still adding mass to the protostar.)