Downloading files within a QCoreApplication

I work in a team to develop a QT Application with c++. Among other things, the app needs to download files from the internet. Here is the code I wrote to download files:

int main(int argc, char *argv[]){
        QCoreApplication app(argc, argv);
        QNetworkAccessManager man;
        std::string urlc = "https://upload.wikimedia.org/wikipedia/commons/7/73/Flat_tick_icon.svg"; //Ramdom svg file
        QUrl url(QString::fromStdString(urlc));
        QNetworkRequest req(url);
        QNetworkReply* reply = man.get(req);
        QObject::connect(reply, &QNetworkReply::finished, [department, region, &reply](){
            QByteArray read = reply->readAll();
            QString savefile = QString::fromStdString("file.png");
            QFile out(savefile);
            out.open(QIODevice::WriteOnly);
            out.write(read);
            out.close();
            reply->close();
            reply->deleteLater();
            app.quit();
        });
        return app.exec();
  }

The above code works well and downloads the file at the specified url. However, if I try to extract the downloading of files to a separate function (see code below), the program doesn't work. In fact, it never even starts downloading the file.

std::string download_file(){
    QNetworkAccessManager man;
    std::string urlc = "https://upload.wikimedia.org/wikipedia/commons/7/73/Flat_tick_icon.svg"; //Ramdom svg file
    QUrl url(QString::fromStdString(urlc));
    QNetworkRequest req(url);
    QNetworkReply* reply = man.get(req);
    QObject::connect(reply, &QNetworkReply::finished, [department, region, &reply](){
        QByteArray read = reply->readAll();
        QString savefile = QString::fromStdString("file.png");
        QFile out(savefile);
        out.open(QIODevice::WriteOnly);
        out.write(read);
        out.close();
        reply->close();
        reply->deleteLater();
    });
    return "file.png";
}

int main(int argc, char *argv[]){
    QCoreApplication app(argc, argv);

    std::string path = download_file();
    std::cout << path << std::endl;

    return app.exec();
}

What can be the reason for such behaviour?