Issue in setting minimum width for a container in flutter

min_width_issue.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        body: GridView.count(
          primary: false,
          padding: const EdgeInsets.all(20),
          crossAxisSpacing: 10,
          mainAxisSpacing: 10,
          crossAxisCount: 2,
          children: <Widget>[
            Container(
              constraints: BoxConstraints(minWidth: 300, minHeight: 300, maxWidth: 300, maxHeight: 300),
              alignment: Alignment.center,
              child: Container(
                constraints: BoxConstraints(minWidth: 300, minHeight: 300, maxWidth: 300, maxHeight: 300),
                height: 300,
                width: 300,
                padding: const EdgeInsets.all(8),
                child: const Text("He'd have you all unravel at the"),
                color: Colors.teal[100],
              ),
            ),
            Container(
              constraints: BoxConstraints(minWidth: 300, minHeight: 300, maxWidth: 300, maxHeight: 300),
              alignment: Alignment.center,
              child: Container(
                constraints: BoxConstraints(minWidth: 300, minHeight: 300, maxWidth: 300, maxHeight: 300),
                height: 300,
                width: 300,
                padding: const EdgeInsets.all(8),
                child: const Text('Heed not the rabble'),
                color: Colors.teal[200],
              ),
            ),
            Container(
              constraints: BoxConstraints(minWidth: 300, minHeight: 300, maxWidth: 300, maxHeight: 300),
              alignment: Alignment.center,
              child: Container(
                constraints: BoxConstraints(minWidth: 300, minHeight: 300, maxWidth: 300, maxHeight: 300),
                height: 300,
                width: 300,
                padding: const EdgeInsets.all(8),
                child: const Text('Sound of screams but the'),
                color: Colors.teal[300],
              ),
            ),
            Container(
              constraints: BoxConstraints(minWidth: 300, minHeight: 300, maxWidth: 300, maxHeight: 300),
              alignment: Alignment.center,
              child: Container(
                constraints: BoxConstraints(minWidth: 300, minHeight: 300, maxWidth: 300, maxHeight: 300),
                height: 300,
                width: 300,
                padding: const EdgeInsets.all(8),
                child: const Text('Who scream'),
                color: Colors.teal[400],
              ),
            ),
            Container(
              constraints: BoxConstraints(minWidth: 300, minHeight: 300, maxWidth: 300, maxHeight: 300),
              alignment: Alignment.center,
              child: Container(
                constraints: BoxConstraints(minWidth: 300, minHeight: 300, maxWidth: 300, maxHeight: 300),
                height: 300,
                width: 300,
                padding: const EdgeInsets.all(8),
                child: const Text('Revolution is coming...'),
                color: Colors.teal[500],
              ),
            ),
            Container(
              constraints: BoxConstraints(minWidth: 300, minHeight: 300, maxWidth: 300, maxHeight: 300),
              alignment: Alignment.center,
              child: Container(
                constraints: BoxConstraints(minWidth: 300, minHeight: 300, maxWidth: 300, maxHeight: 300),
                height: 300,
                width: 300,
                padding: const EdgeInsets.all(8),
                child: const Text('Revolution, they...'),
                color: Colors.teal[600],
              ),
            ),
          ],
        ),
      ),
    );
  }
}