Stereotypically, gender is also cited as one of the reasons why people like to gamble. One of the research findings In gambling, generally, women don't like it when others see them lose. Girls probably prefer slot machines because no one sees players win or lose.
Gambling with slot machines is often a personal experience free of guilt or shame. While the men are not like that.
I strongly agree with you on this. I might not have meet girls who play slot games but I know how most female friends react to loses when the play indoor games with me or my friends. The get so ashamed to lose sometimes the beg the male players to allow them win so they can brag with it. I think it will be the same reason females prefer slot games since it free from shame and guilt, most females in my neighbourhood who gamble are always shy of visiting the gambling house too, most of the times the prefer to be accompanied to help reduce the shyness, I don't know if this too will be attributed to the fear of losing or the don't want to be seen as a gambler.