Currently when a composer package can't be updated it shows a message indicating that there are restrictions. It would be nice to add additional information that helps developers to know why the package can be updated.
Proposed resolution
Showing the full error message may pollute the drupal updater output, but we can suggest the user how to debug it. Add a message proposing running the composer require command with the --dry-run option. SOmething like this:
For more information, run: composer require vendor/package:^<latest_version> -W --dry-run