Interesting note - if product reviews are enabled at store level (in WooCommerce settings) then the option at product level is ticked by default when a product is added. If the option is disabled at store level then it's unticked by default at product level. When you update the setting at store level it doesn't update product settings so they need to be manually updated, but going forward any new products will have the same setting as whatever is set in WooCommerce, and.you can use the product level setting to disable reviews for individual products.