Can rewrites fallback if 404? Rewrite conflict issue

I have pages and product categories on my site:

Pages:
--About
--Contact
Products:
--Category 1
----Subcategory 1
--Category 2

Ideally I want mysite.com/category-1/subcategory-1 to show the product category page and mysite.com/about to show a normal page. I have registered the taxonomy in the following way:

function products_taxonomy() {
    register_taxonomy(
        'product_categories',
        'product',
        array(
            'hierarchical' => true,
            'label' => 'Product Categories',
            'query_var' => true,
            'rewrite' => array(
                'hierarchical' => true,
                'slug' => "https://wordpress.stackexchange.com/",
                'with_front' => false
            )
        )
    );
}
add_action( 'init', 'products_taxonomy');

Currently, the category URL is working, but the page URL eg mysite.com/about/ is 404ing.

I have installed the Rewrite Analyzer plugin and I can see this is because WordPress is only checking for a product category called “about”, which it can’t find, hence the 404. It is not checking subsequent rewrite rules. Is there a way I can catch this 404 and get WordPress to check the next rewrite rule instead of immediately showing a 404? I’m a bit confused as to why this is not the default behaviour…