Many well known brands and manufacturers want you to try their new products for free. Manufacturers hope that after you try their product for the first time, you will like it and will start purchasing it.
Market research is the reason why manufacturers send free samples in the mail to people like you. Companies spend months and hundreds of thousands on designing and developing new products.
Other companies force you to sign up for email lists in order to receive products, but that is not the case here. You can be assured that you will not be spammed with irrelevant offers.