Doesnt Flutter showDialog works in stateFul state?

I am new at Flutter. I am trying to have a floatingActionButton which will open a showDialog box when pressed. But at the first code it doesn’t do anything and at debug console at vscode the error is

════════ Exception caught by gesture ═══════════════════════════════════════════ No MaterialLocalizations found.

But I found the second code working correct. Would you please point out the issue with the first code. Thank you.
1st Flutter code:

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  Future _incrementCounter() => showDialog(
      context: context,
      builder: (context) => AlertDialog(
            title: Text("alert"),
          ));

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        floatingActionButton: FloatingActionButton(
          onPressed: _incrementCounter,
          elevation: 0,
          child: Icon(Icons.add),
        ),
      ),
    );
  }
}

2nd Flutter code:

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Future _incrementCounter() => showDialog(
      context: context,
      builder: (context) => AlertDialog(
            title: Text("data"),
          ));

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

After the error , I created new project (2nd one) and tried to do the same thing and worked fine. I guess there is a problem with sateless – stateful.