I think that's exactly it. There's nothing in their contracts that says they must sell the product through them. In fact, you can't have exclusive distribution rights because then the others couldn't.I don't see anything illegal or immoral about selling your product directly to consumers.
This is no different than Apple selling phones at AT&T stores but also selling direct. Or Levi's selling jeans at Macy's but also having a website. Or Nike. Or. Sony. Basically almost every electronics and clothing manufacturer does this.