Describe the bug
If migration requirements are not met, then the following message is visible in Drush logs:
[debug] Migration 'foo' is skipped as its source plugin has missed requirements: . [0.13 sec, 24.65 MB]

Requirements details are missing. Let's look at this code to understand why:

foreach ($migrations as $migrationId => $migration) {
    try {
        $sourcePlugin = $migration->getSourcePlugin();
        if ($sourcePlugin instanceof RequirementsInterface) {
            $sourcePlugin->checkRequirements();
        }
    } catch (RequirementsException $exception) {
        $this->logger()->debug("Migration '{$migrationId}' is skipped as its source plugin has missed requirements: " . $exception->getRequirementsString());
        unset($migrations[$migrationId]);
    }
}

The problem is at $exception->getRequirementsString(), which returns an information about requirements array passed into the exception. This array is supposed to provide additional metadata and probably shouldn't be visible for developers. At least, I don't see any value in this information. That's why I opened a drupal.org issue to adjust the message format as well: https://www.drupal.org/project/drupal/issues/3254986. Feel free to check it out to see more details.

Speaking of Drush commands, if requirements were passed as 2nd argument, the message is the following:
Migration 'd6_comment' is skipped as its source plugin has missed requirements: source_module: comment.

Otherwise, the message is:
Migration 'user_profile_field_instance' is skipped as its source plugin has missed requirements: .

To Reproduce

1. Install latest Drupal core (9.4.x);
2. Install Migrate Drupal module;
3. Run drush ms user_profile_field_instance -vvv

Expected behavior
I would expect the following message (with or without the requirements array):
Migration 'd6_comment' is skipped as its source plugin has missed requirements: The module comment is not enabled in the source site.

Actual behavior
Migration 'd6_comment' is skipped as its source plugin has missed requirements: source_module: comment.