Get WooCommerce product category list in functions.php

I am trying to create a an array of WooCommerce product categories to use as a dropdown in the Customizer. The following code is working in a function hooked to ‘customize_register’ but not in functions.php

Unfortunately I need to create an array in functions.php

$woo_cat_args = array(
    'taxonomy'     => 'product_cat',
    'orderby'      => 'name',
    'hide_empty'   => 0,
);
$woo_categories = get_categories( $woo_cat_args );

In functions.php I am getting an empty array, but in the function hooked to ‘customize_register’ I am getting the WooCommerce categories.

So how can I get the categories in functions.php?