Because injecting Environment is more discoverable and a better DX than injecting AppConfig.

public function __construct(
    private readonly Environment $environment,
) {}

EDIT: so actually, as specified in my comment below, I completely dissociated AppConfig from Environment:

• The booting process uses Environment::fromEnv indirectly through AppConfig's constructor when resolved from the container
• Specifying the environment property of the AppConfig in userland will not behave as expected due to that
• It makes sense that Environment is its own source of truth in the container, it's even easier to spoof in tests