Dropdown box in Flask App using WTForms not updating

I have a flask web app with a Customer page and a Project Page. This is the workflow and where it goes wrong. Any ideas where I might have gone wrong?

1. View customer page
2. Click "Add Customer" > taken to "add_customer" route
3. Add customer info and click submit
4. Customer page is updated correctly with latest customer name
5. View Projects page
6. Click "Add Project" > taken to "add_project" route
7. This page has a dropdown box for list of customer but does not include the last customer I created or any customers I have created since I last started flask.

If I restart flask, the dropdown box contains the latest customers. At first I thought I was not committing the database, but it seems like I am with the db.session.commit below. I posted relevant code, let me know if you want to see anything else.

I can't seem to find my particular issue on the web, most of what I find pertains to filling in the dropdown box itself, which does work.

forms.py:

class AddProjectForm(FlaskForm):
    projectname = StringField('Project Name', validators=[DataRequired()])
    customer_query = Customer.query.all()
    customers = []
    for c in customer_query:
        customers.append(c.customername)
    customers = SelectField('Customer', choices=customers, default=1)
    submit = SubmitField('Add Project')

routes.py:

@app.route('/add_customer', methods=['GET', 'POST'])
@login_required
def add_customer():
    customer = Customer.query.all()
    form = AddCustomerForm()
    if request.method == 'POST':
        customername = request.values.get('customername') 
        c = Customer(customername=customername)
        db.session.add(c)
        db.session.commit()
        return redirect(url_for('customer'))
    return render_template("add_customer.html", title='Add a Customer', form=form)

@app.route('/add_project', methods=['GET', 'POST'])
@login_required
def add_project():
    form = AddProjectForm()
    if request.method == 'POST':
        projectname = request.values.get('projectname') 
        customer = request.values.get('customers') 
        customer_id = Customer.query.filter_by(customername=customer).first().id
        project = Project(projectname=projectname,customer_id=customer_id)
        db.session.add(project)
        db.session.commit()
        return redirect(url_for('projects'))
    return render_template("add_project.html", title='Add a Project', form=form)

add_project.html

{% extends "base.html" %}

{% block content %}
    <h1>Add a Project</h1>
    <form action="" method="post">
        {{ form.hidden_tag() }}
        <p>
            {{ form.projectname.label }}<br>
            {{ form.projectname }}<br>
        </p>
        <p>
            {{ form.customers.label }}<br>
            {{ form.customers }}<br>
        </p>
        <p>
            {{ form.submit() }}
        </p>
    </form>
{% endblock %}