This explains why the astronomers did not revise their mass estimates by much. If a large majority of the universe’s mass is not contained in galaxies, then finding new galaxies would not be cause to update the mass measurement by a significant amount.

This does not explain why astronomers chose not to update their mass estimates. If the masses of the new galaxies can at least be estimated, their mass should have been added to estimates of the total mass of the universe.

This gives context for the astronomers’ discovery, but does not explain why they opted to keep their current mass estimates. If astronomers routinely discover new galaxies, their estimates of the universe’s mass should also be updated routinely.

This is irrelevant information. Astronomers did not update their estimates of the universe’s total mass, so theories about galaxy development would not have been so affected anyway.

This does not state that some astronomers disregard the number of galaxies when estimating the universe’s total mass. Whatever their methods, their decision not to update their measurements is a mystery.