Here's why:
* Diligence refers to the quality of being hardworking and careful. It's a singular concept.
* Honesty refers to the quality of being truthful and sincere. It's also a singular concept.
To make them plural, you would add an "s" at the end:
* Diligences: (Multiple instances of hardworking efforts)
* Honesty's: (This is less common but can be used in specific contexts, like "honesty's importance" to emphasize the importance of honesty)