Partly because it was the standard when huge advances were being made in astrophysics in the late 19th/early 20th C. Partly, because some formulae are more conv

Partly because it was the standard when huge advances were being made in astrophysics in the late 19th/early 20th C. Partly, because some formulae are more convenient to use in cgs than in SI, because cgs is not rationalized and SI is.