Why activity manager is returning one recent app on android phone but all on genymotion?

Question

I looked into some code to get the recent apps in my phone. it is working fine on genymotion but not on android phone.here is the code.

package com.example.abdul.myapplication;
import java.util.List;
import android.app.ActivityManager;
import android.app.ActivityManager.RunningAppProcessInfo;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.TextView;

 public class MainActivity extends AppCompatActivity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    TextView tv = (TextView) findViewById(R.id.textView);

    ActivityManager activityManager = (ActivityManager) this
            .getSystemService(ACTIVITY_SERVICE);

    List<RunningAppProcessInfo> procInfos = activityManager
            .getRunningAppProcesses();
    for (int idx = 0; idx < procInfos.size(); idx++) {

        tv.setText(tv.getText() + "" + (idx + 1) + "."
                + procInfos.get(idx).processName + "\n");

    }

    }
    }