What if I told you that SCOTUS has previously acknowledged that corporate (negative) speech deserves less protection than citizen (positive) political speech?
This is why state governments can require that companies put warning labels or nutritional information on their products, which would otherwise be considered compelled speech.
Because the publisher is choosing to publish based on the identity or opinions of the customer.
To give another controversial example, there's a difference between a manufacturer choosing not to produce customized cakes, and a manufacturer choosing not to produce cakes customized for interracial couples.