Fall through the cracks

1. to not be noticed or dealt with

2. To go unnoticed or undealt with; to be unintentionally neglected or ignored, especially in a corporate, political, or social system.

Because so many other social issues take priority for the government, such as drug addiction and unemployment, the welfare of children in the foster system very often ends up falling through the cracks.We were all so busy drawing up the contracts for this new deal that the thank-you dinner we'd promised to our interns simply fell through the cracks.