android - アプリケーション プロセスが強制終了された後にサービスが再起動される理由

Question

サービスを開始する次のコードがあります。

package com.example.serviceapp;

import android.app.Service;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.IBinder;
import android.util.Log;
import android.widget.Toast;

public class MyService extends Service {
    private static final String TAG = "MyService";
    MediaPlayer player;

    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public void onCreate() {
        Toast.makeText(this, "My Service Created", Toast.LENGTH_LONG).show();
        Log.d(TAG, "onCreate");

        player = MediaPlayer.create(this, R.raw.music);
        player.setLooping(false); // Set looping
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Toast.makeText(this, "My Service Started", Toast.LENGTH_LONG).show();
        Log.d(TAG, "onStart");
        player.start();

        /*
         * START_STICKY: Constant to return from onStartCommand(Intent, int,
         * int): if this service's process is killed while it is started (after
         * returning from onStartCommand(Intent, int, int)), then leave it in
         * the started state but don't retain this delivered intent.
         */
        return START_STICKY;
    }

    @Override
    public void onDestroy() {
        Toast.makeText(this, "My Service Stopped", Toast.LENGTH_LONG).show();
        Log.d(TAG, "onDestroy");
        player.stop();
    }

}

しかし、アプリケーション プロセスが強制終了されると、サービスが停止し、再び開始されるのはなぜですか?

これは、サービスを開始/停止する方法です:

public class MainActivity extends Activity {
    private static final String TAG = "ServicesDemo";
    Button buttonStart, buttonStop;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        buttonStart = (Button) findViewById(R.id.buttonStart);
        buttonStop = (Button) findViewById(R.id.buttonStop);

        buttonStart.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                Log.d(TAG, "onClick: starting srvice");
                startService(new Intent(getApplicationContext(),
                        MyService.class));
            }
        });
        buttonStop.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                Log.d(TAG, "onClick: stopping srvice");
                stopService(new Intent(getApplicationContext(), MyService.class));
            }
        });
    }

}