On a single product page under the tabs the related products are shown. Selection is based on the set of product with one similar tag or category (see function get_related in abstract-wc-product.php in woocommerce/classes/abstracts). So every product with a slight similarity could be shown here.
Wouldn’t it be more appropriate that the products with all tags and all categories are shown here?
Is it possible to change this in a future release?