Form doesn't appear when mixing DetailView and FormView in single view

I am following this https://docs.djangoproject.com/en/3.0/topics/class-based-views/mixins/#an-alternative-better-solution so that for ever Book detail view users can post reviews below.

class BookDetailView(DetailView):
    model = Book

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context['form'] = BookReviewForm()
        return context

class BookComment(SingleObjectMixin, FormView):
    template_name = 'book/book_detail.html'
    form_class = BookReviewForm
    model = Book

    def post(self, request, *args, **kwargs):
        if not request.user.is_authenticated:
            return HttpResponseForbidden()
        self.object = self.get_object()
        return super().post(request, *args, **kwargs)

    def get_success_url(self):
        return reverse('book_detail', args=[str(self.object.id)])

class BookDetail(View):

    def get(self, request, *args, **kwargs):
        view = BookDetailView.as_view()
        return view(request, *args, **kwargs)

    def post(self, request, *args, **kwargs):
        view = BookComment.as_view()
        return view(request, *args, **kwargs)

The form used is:

class BookReviewForm(forms.Form):
    class Meta:
        model = Review
        fields = ('review', 'score',)

The Review model:

class Review(models.Model):
    book = models.ForeignKey(
        Book,
        on_delete=models.CASCADE,
        related_name='reviews',
    )
    review = models.CharField(max_length=5000)
    score = models.PositiveSmallIntegerField(null=True, blank=True,
                                             validators=[MinValueValidator(0), MaxValueValidator(10)])
    author = models.ForeignKey(
        get_user_model(),
        on_delete=models.CASCADE,
    )

    class Meta:
        unique_together = ('book', 'author')

    def __str__(self):
        return self.review

Yet when I add the form to the template:

<div>
            <form method="POST">{% csrf_token %}
        {{ form.as_p }}
        <button type="submit">Send</button>
    </form>
        </div>

it doesn't appear, only the submit button. If I click the button, I get redirected correctly. How can I make the form appear?

class BookReviewForm(forms.ModelForm):
    class Meta:
        model = Review
        fields = ('review', 'score',)

Please change the form to model form