Because if you tried to actually police this then everything in life would grind to a halt. It would be like expecting the government to deal with every single crime.
It's particularly problematic when a business is providing a platform for other entities to post a message. We don't hold the post office liable for transferring copyrighted/trademarked content, do we?
This case is more akin to a TV network, since the ad is publicly broadcasted based on what people are watching/reading. It’s not private correspondence.
It's particularly problematic when a business is providing a platform for other entities to post a message. We don't hold the post office liable for transferring copyrighted/trademarked content, do we?