Why Third Row widget in the Column stack goes away?

Question

I am building the app where my widget tree starts with Scaffold and as for body parameter, I assign the column widget. Within the column widget, I want the first 3 buttons sitting side by side, which work fine and next Expanded Widget which takes whole screen and third again 2 buttons sitting side by side. However, the thing is that, the third row widget is not visible on the screen of the phone. Can someone explain why it happens?

 Scaffold(
      appBar: AppBar(
        title: const Text("My Work Timer"),
      ),
      body: Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          Row(
            children: [
              Padding(padding: EdgeInsets.all(defaultPadding)),
              Expanded(
                child: ProductivityButton(
                    color: const Color(0xff009688),
                    text: "Work",
                    size: 3,
                    onPressed: () {}),
              ),
              Padding(padding: EdgeInsets.all(defaultPadding)),
              Expanded(
                child: ProductivityButton(
                    color: const Color(0xff607D8B),
                    text: "Short Break",
                    size: 3,
                    onPressed: () {}),
              ),
              Padding(padding: EdgeInsets.all(defaultPadding)),
              Expanded(
                child: ProductivityButton(
                    color: const Color(0xff455A64),
                    text: "Long Break",
                    size: 3,
                    onPressed: () {}),
              ),
              Padding(padding: EdgeInsets.all(defaultPadding)),
            ],
          ),
          Expanded(
            child: Text("Hello"),
          ),
          Row(
            children: [
              Padding(padding: EdgeInsets.all(defaultPadding)),
              Expanded(
                  child: ProductivityButton(
                color: const Color(0xff212121),
                size: 2,
                text: "Stop",
                onPressed: () {},
              )),
              Padding(padding: EdgeInsets.all(defaultPadding)),
              Expanded(
                  child: ProductivityButton(
                color: const Color(0xff009688),
                size: 2,
                text: "Restart",
                onPressed: () {},
              )),
              Padding(padding: EdgeInsets.all(defaultPadding)),
            ],
          )
        ],
      ),
    );

regards