Facebook appid is not passing why?

Question

 <application
    android:allowBackup="true"
    android:hardwareAccelerated="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/Theme.AppCompat.NoActionBar"
    >



    <activity
        android:name=".MainActivity"
        android:hardwareAccelerated="true">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>


    </activity>

    <service
        android:name=".Life"
        android:enabled="true"
        android:exported="true"></service>

    <meta-data
        android:name="com.google.android.gms.games.APP_ID"
        android:value="@string/app_id">

    </meta-data>
    <meda-data
        android:name="com.facebook.sdk.ApplicationId"
        android:value="@string/facebook_app_id" />

</application>

Continuing my question that is here linked LoginButton facebook android NullPoiunterExecptioi today i tried adding this line of code under FacebookSdk.sdkInitialize(getApplicationContext());

FacebookSdk.setApplicationId(getResources().getString(R.string.facebook_app_id));

and how it works so my question is if i passed correctly the facebook_app_id in the manifest inside application tag why it only works if i set it from code(?) please help me thanks indeed.