The issue is that Amazon is the largest online retailer in the world and they are refusing to carry items that compete with their other business units.

Your example misses the point. People reasonably expect Amazon to carry electronics. Amazon is abusing their position as the largest retailer in world to suppress competition. That's illegal.

But with your example, Ford does not control 90% of car dealers in the US, so they are not in a position of power. Now, if Ford owned 90% of car mechanics in the US and they refused to repair Chevys, that would be abusing their position of power to suppress competition.