Every protein is assumed to be surrounded by a Solvent that consists mainly of water. The presence of water means that a protein tends to be more stable if the Hydrophobic (literally, "water fearing") residues are buried in the core.
In Foldit, the solvent is not visible. The effect of water and other molecules randomly bouncing of the protein would be extremely complex to model (a very powerful computer would be needed). Foldit does not attempt to simulate the effects of the solvent as you shake or wiggle the protein.