Refactoring InputDecoration does not reproduce behaviour

gistfile1.txt

import 'package:flutter/material.dart';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Column(
          children: [PasswordField1(), PasswordField2()],
        ),
      ),
    );
  }
}

class SignInDecoration extends InputDecoration {
  SignInDecoration(BuildContext context, {Widget suffixIcon, String hintText})
      : super(hintText: hintText, suffix: suffixIcon);
}

class PasswordField1 extends StatefulWidget {
  const PasswordField1({this.hintText, this.decoration});

  final String hintText;
  final InputDecoration decoration;
  @override
  _PasswordField1State createState() => new _PasswordField1State();
}

class _PasswordField1State extends State<PasswordField1> {
  bool _obscureText = true;

  @override
  Widget build(BuildContext context) {
    return TextFormField(
      obscureText: _obscureText,
      decoration: SignInDecoration(
        context,
        hintText: 'Password',
        suffixIcon: GestureDetector(
          onTap: () {
            setState(
              () {
                _obscureText = !_obscureText;
              },
            );
          },
          child: Icon(_obscureText ? Icons.visibility : Icons.visibility_off),
        ),
      ),
    );
  }
}

class PasswordField2 extends StatefulWidget {
  const PasswordField2({this.hintText, this.decoration});

  final String hintText;
  final InputDecoration decoration;
  @override
  _PasswordField2State createState() => new _PasswordField2State();
}

class _PasswordField2State extends State<PasswordField2> {
  bool _obscureText = true;

  @override
  Widget build(BuildContext context) {
    return TextFormField(
      obscureText: _obscureText,
      decoration: InputDecoration(
        hintText: 'Password',
        suffixIcon: GestureDetector(
          onTap: () {
            setState(
              () {
                _obscureText = !_obscureText;
              },
            );
          },
          child: Icon(_obscureText ? Icons.visibility : Icons.visibility_off),
        ),
      ),
    );
  }
}