Why default lines for One2many fields are not filling in related and default values automatically in Odoo 13?

I have a button in the model sale.order with executes the method action_open_certification_views. This method opens the sale.certification tree view. So the method returns the dictionary of the action which opens the sale.certification views, and I have added the following context to auto-fill in the sale.certification fields (sale_id and line_ids, where line_ids is a One2many field pointing to sale.certification.line):

def action_open_certification_views(self):
    ...
    action['context'] = {
        'default_name': 'My Certification',
        'default_sale_id': self.id,
        'default_line_ids': [
            (0, 0, {
                'quantity': 5.0,
                'sale_line_id': line.id,
            }) for line in self.order_line
        ],
    }
    return action

When I click on the button, the sale.certification tree view is opened right, and if click on Create button, the context of the action is working well since I see the sale.certification form filled in automatically with the default name My Certification, the right link to sale order, and the same number of certification lines as sale order lines has the sale order. Each of this certification lines has quantity 5.0, and the link to sale order line is right too.

The problem is that the sale.certification.line model has many other fields which are related or which have default values, but these certification lines filled in by default by the action context are not filling in those fields.

For example, there is another field quantity2 in sale.certification.line model, and visible in the view, which always takes by default 1.0. However, the field is empty in all default lines. Same problem with related fields. There are some related fields in the view which take their values through sale_line_id field. These one is filled in OK, but the related fields remain empty. For example, in `sale.certification.line model there is this field:

product_uom = fields.Many2one(
    related='sale_line_id.product_uom',
)

In spite of having sale_line_id filled in OK in all lines, they have product_uom empty. Can anyone tell me why? Do I have to specify their values in context too, despite they should have been filled in by theirselves?