Symbolism, Imagery, Allegory
When Turtle first arrives in Key West, it's downright weird to her that no one wears shoes. She still puts hers on every morning—not because her feet stink or anything like that, but because they are important to her. Check out how she describes getting the shoes in the first place:
I loved those shoes. I remember the day Archie bought them for me. He'd taken Mama and me out to lunch at the counter at Woolworth's. After, Mama was buying me a pair of glue-on soles to help stretch my too-small shoes when Archie stopped her. "The princess needs new shoes," he said. "That's all there is to it." (12.2)
Okay, so Archie bought the shoes for Turtle in a very family-friendly moment. He's setting himself apart from all her mother's other suitors by giving Turtle fancy shoes, and it makes her feel special and loved. She even confides in us that it's something a father would do. So the shoes become more than just things she puts on her feet. They represent the potential for a family that includes Turtle, Archie, and her mom.
It makes sense, then, that after living with her relatives in Florida for a bit, she no longer has a place for the shoes. She finds it a little weird, but she claims:
Strange as it sounds, I'm having a hard time getting used to wearing them. They're pretty as a postcard, but they pinch my toes and my feet are hot and sweaty. (17.57)
It's important that we understand that Turtle has transformed into a Conch herself over the course of the book. At first she thought it was silly not to wear shoes; now she thinks the opposite. And hey—at first she thought Archie was dad material, but by the time the book ends, she thinks the opposite about him as well.
Besides, she doesn't have room for the promises of fancy things that Archie once made her. Now she's all about the simple life. No shoes required.