Why does Hulga go on the picnic with Manley Pointer in "Good Country People"?

Hulga is Mrs. Hopewell’s only child. She is thirty-two years old and is highly educated. She has a PhD in Philosophy, and most of the villagers find her attitude quite incomprehensible. Mrs. Hopewell still likes to treat Hulga like a child and refuses to call her by her legal name, which she finds as ugly as the “hull of a battleship.” Hulga has to stay close to her mother because she has a weak heart. The doctors think that with the best of care, she might just be able to see her forty-fifth birthday.
Hulga is openly discourteous to Manley Pointer, the Bible salesman when he visits her house. Mrs. Hopewell invites Manley to stay for dinner with them after discovering that the nineteen-year-old Bible salesman has a heart condition similar to Hulga’s. Throughout dinner, Hulga ignores the boy and seems quite put off by his poor dining etiquette. It is therefore strange that Hulga walks the boy out and even agrees to meet him the following day for a picnic. Considering the kind of conversation the two have before their walk, one wonders why the highly educated Hulga tolerates the boy. The boy’s speech sounds like absolute gibberish, and his first question to Hulga is whether she has ever eaten a two-day-old chick, after which he bursts into giggles like a child. The boy asks her how old she is, and she lies, saying that she is seventeen years old. The boy thinks that Hulga is simply shy and that the two can make a great couple.
It is not stated why Hulga is willing to go out on a date with Manley. Perhaps she is attracted to the illiterate boy, for she spends half of the night thinking about her conversation with him. As she says, “Genius can get an idea across even to an inferior mind.” Perhaps she hopes to have stimulating discussions with him; she might be able to teach him a thing or two about life. Another reason could be because she thinks that Manley is a simple boy whom she can control and who does not know much about the world—especially since he is a saved Christian, one of the “good country people.” She also seems to like the idea that it is her who is seducing the “innocent” Manley. She really is attracted to his innocence.
The story takes a weird turn toward the end when Hulga realizes that Manley is a phony, a sexual pervert who drifts from place to place while collecting trophies from his sexual conquests. He takes off with Hulga’s artificial leg after she rejects his advances.