Why can't the buttons in the column be full-width, but the outside buttons can be full-width?

These are two identical buttons
The width of the outer button is the same as the width of the page
The width of the inner button is the smallest possible width
I want the inner button to be the same width as the card, how do I change this?
How do I update?

import 'package:flutter/material.dart';

class RoomListPage extends StatefulWidget {
  const RoomListPage({Key? key}) : super(key: key);

  @override
  _RoomListPageState createState() => _RoomListPageState();
}

class _RoomListPageState extends State<RoomListPage> {
  List roomList = [
    {
      "title": "bedroom",
      "type": "bedroom",
      "description": "this is bedroom",
    },
    {
      "title": "kitchen",
      "type": "kitchen",
      "description": "this is kitchen",
    },
    {
      "title": "bathroom",
      "type": "bathroom",
      "description": "this is bathroom",
    },
  ];
  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(20.0),
      child: ListView(children: [
        const SizedBox(height: 20),
        ElevatedButton(onPressed: () {}, child: const Text('Add region')), // outer button - full width
        const SizedBox(height: 20),
        ...roomList.map(
          (room) => Column(
            children: [
              ElevatedButton(onPressed: () {}, child: const Text('Add region')), // inner button - min width
              Card(
                  child: Column(
                children: [
                  Text(room['title'] as String),
                  Text(room['description'] as String),
                ],
              )),
              const SizedBox(height: 20)
            ],
          ),
        ),
      ]),
    );
  }
}

Try wrapping the ElevatedButton in a Row. You can learn more about Flutter constraints at https://docs.flutter.dev/ui/layout/constraints