They care for many reasons. Hence let's say they have a lot of inventory pertaining to a certain kit, etc. Bad reviews can hamper sales especially sales to potential buyers whom have no knowledge of the product.
People have stated they will change their reviews when they recieve the part and thus the issue resolved. Pretty simple for a retailer to obtain positive reviews by simply providing the part(solution).
Reviews really don't matter to the the experienced consumer per product of interest but to the consumer whom has no real knowledge or experience, reviews being positive or negative per product of interest can weigh heavily on what may be purchased.
Consumer reviews are usually what triggers companies to improve on a product, terminate a product and so on.