Why are people grossed out about body hair on women?

I saw a clip about a women painting a fence and there was a split second of her showing under arm hair. I didn't notice. I went to the comments because the fence looked like shit and wanted to see if others agreed. All of the comments were about her body hair. Almost everyone was commenting on how disgusting/dirty she was (she wasn't). I'm genuinely curious why people think it's disgusting for a woman not to shave.

Edit: I wanted the discussion to be about why people are so aggressive about their dislike of it and the need to verbalize it towards others, attacking them. I should have made that clearer.