Why did military recruiter lie to someone who was volunteering to join?

Know this woman who was in the military many years ago. She told me that her Navy recruiter lied to her. She wanted to be an Airedale (airplanes) but the recruiter told her that he was going to enlist her as a seaman ( ships) so she could go in sooner and that when she got to boot camp she could switch over to the other, aviation. When she got to boot camp, she was told this was not possible because she had already signed the papers and enlisted as a seaman. She said her initial plan was to retire from the military but that it changed once she got to her first command station as a deck person. She said she just about lost her mind at her first duty station which had a reputation for being a bad assignment. Question is: why would a recruiter lie to someone who was VOLUNTEERING to go fight for their country? If people did not volunteer, they would have to draft them instead. Why mislead and lie when they are already wanting to go?