Why do people keep mentioning gift giving at the bachelorette party?

It is probably regional or just something among different groups of friends. My niece gave a bachelorette party/lingerie shower for a friend of hers. They did bring gifts, but it was clear that it was a shower AS WELL as a party. Personally, if I was invited to a Bachelorette Party, I wouldn't take a gift unless someone clued me in that it was expected.....