Fitch brushes are/were very expensive. Bear hair was often used in its place as a fine brush for bromoil.
Don't know which would be worse, trying to get a polecat or a bear to give you a little hair for a brush!
Still have both the hog and bear brushes that I bought back in the 80s from a French company that is no longer in business, they were expensive then so I can only imagine what they would cost now.
Hog hair is used for the early stages of inking an/or for a course look, bear brushes give finer detail and lower the contrast somewhat. You kind of need both types.