My problem set solution cites:
"Although sulfur is less electronegative than oxygen, overlap is a more important consideration. Sulfur is a member of the third period. As a consequence, a sulfur atom is larger than an oxygen atom and the C–S bond is longer than the C–O bond, contributing to poorer overlap."
However, I don't quite understand why a longer bond length would contribute to poor orbital overlap, and how greater overlap contributes to more stability.