Why does Django REST have serializers, can't forms perform the same function?

Question

I am working through the Django REST tutorial, and I don't see the benefit of serializers, I feel like I must be missing something:

Client Side

Django REST is for Ajax calls. On the client side, if one would like a JSON version of a Form, one can perform:

    const FORM = document.querySelect('form');
    const formData = new FormData(FORM);
     const init = {
        body: formData,
        method: "post",
     };
     const response = await fetch(url, init);

This is the JSON version of the form that can be fetch POST'ed via AJAX to Django REST.

Server Side

Say I have a dictionary of values, and I wish to check one can make a valid object from it:

# Forms
FormClass(data=data).is_valid()
# Serializer
Serializer(data=data).is_valid()

Say I have a dictionary of posted values, and I wish to create an object from them

# Forms
FormClass(data=data).save()
# Serializer
Serializer(data=data).save()

Say I have a form/serializer instance, and I wish to have a JSON representation:

# Forms
json.dumps(form.data)
# Serializer
json.dumps(serializer.data)

I can give similar examples as above for update/delete operations.

For the view, we don't need serializers again:

from rest_framework.views import APIView

class FooView(APIView):
    def post(self, request, **kwargs):
        form = FooForm(request.data)
        if form.is_valid():
            form.save()

As shown above, one can use forms to perform these actions, with the added benefit of they can be rendered in templates, so why use Serializers over forms?