QAbstractItemView::indicator not working properly

#include <QtWidgets>

class TestModel : public QAbstractListModel
{
    Q_OBJECT
public:
    explicit TestModel(const QList<QString>& vals, QObject *parent = nullptr) : QAbstractListModel(parent), vals_{vals}{}

    int rowCount(const QModelIndex &parent = QModelIndex()) const {
        Q_UNUSED(parent)
        return vals_.size();
    }
    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const {
        if (!index.isValid())
            return QVariant();

        switch(role) {
        case Qt::DisplayRole:
            return vals_.at(index.row());
        case Qt::CheckStateRole:
            return Qt::Unchecked;
        default:
            break;
        }
        return QVariant();
    }

private:
    QList<QString> vals_;
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QListView view;
    view.setWindowTitle(qVersion());
    view.setModel(new TestModel(QList<QString>{QStringLiteral("11111"), QStringLiteral("22222"), QStringLiteral("33333")}, &view));
    view.setStyleSheet(QStringLiteral("QAbstractItemView::indicator { width: 6px; height: 6px; border: 1px solid black;}"));
    view.show();

    return a.exec();
}

#include "main.moc"