View model works only in the theme layout issue

I’ve made this file: catalog_category_view.xml in the app/code/Namespace/Products/view/frontend/layout/ folder , with this content:

<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="1column" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
    <body>
        <referenceBlock name="category.products.list">
            <arguments>
                <argument name="viewModel" xsi:type="object">NamespaceProductsViewModelListProductStock</argument>
            </arguments>
        </referenceBlock>
    </body>
</page>

In the list.phtml I have this:

$viewModel = $block->getData('viewModel');
echo $viewModel->getTest();

and I am getting an error that it doesn’t know about the getTest() method. But if I add my xml code for the view model in the app/design/frontend/Magento/MyTheme/Magento_Catalog/layout/catalog_category_view.xml, it works! Why ? Why I cannot use my view model xml code in my custom module ?

Also if I add this code: <referenceBlock name="category.products.list" remove="true"/> in the app/code/Namespace/Products/view/frontend/layout/catalog_category_view.xml, it works. So not sure why the view model doesn’t work .

Thanks