Xcode target Deployment Target vs. project Deployment Target

Target settings override project settings. Project settings are valid for all targets whose settings haven't been overridden.

The iOS Deployment Target on the Project page is the default for all targets in the project. The iOS Deployment Target on each project is an optional project-level override.

To set a target to inherit from the project, you can't use the "General → Deployment Info" section. Instead, go to "Build Settings → Deployment", and for "iOS Deployment Target" choose "Other..." and enter $(inherited).