They’re disabled either globally or on that specific product, your theme doesn’t display the comment section, or a plugin/cache is interfering. Quick fixes are to ensure WooCommerce → Settings → Products → Enable reviews is on, check that the product allows comments in the Discussion box, clear all caches, ulta card balance and test with a default theme.
There is a good amount of understanding in this section, which includes useful knowledge. Play Wacky Flip, a free game where you flip a ragdoll.