If you have a rock separated by a distance of 1 cm to another rock say, both rocks are 1 gram, the gravitational field of each rock is not compounded by the other. The gravitational field of a 1 cm diameter rock of 1 gram is so tiny that it will never overlap the gravitational field of the other rock producing a magnified effect.
Magnified should be the key word here. Think "magne-tism" can magnify the effect, because magnetism is a much greater a force than gravity, but the gravitational fields of the two pebbles are so tiny, that they literally need to be touching each other first before any real effect is measurable.
You know what this means? It means that unless rocks are already touching each other, then their combined gravitational fields will never cause them to stick together. This means that interstellar clouds will remain as such indefinitely unless magnetism is introduced or charged material.
We know gravitational collapse to birth stars is bogus, it can't even clump together two 1 cm sized pebbles. In actuality it does not matter how many pebbles you have, their combined gravitational fields are essentially non-overlapping, meaning there is no combined effect.
Gravitational collapse only takes effect when the fields of the material overlap (the material is touching other material).
Gravitational collapse does not happen absent a gravitating body already present. Worded another way, gravitational collapse can only happen in a closed body. Open bodies cannot gravitationally collapse.