Not necessarily true. You have to challenge it to find out if it's enforceable in many scenarios, and it might act as a deterrent as well. Even a widely known unenforceable clause can deter someone who doesn't previously know that it is unenforceable from doing the action that the clause prohibits. So I can definitely see plenty of reasons to include these types of things in a contract. Plus, what does it cost them to include it in the contract?

> If such a thing wasn't enforceable Google and others wouldn't be putting it in their contracts.

This is simply false. Almost every contract signed in the US contains unenforceable language. The vast majority of people signing these contracts simply believe that if it's there, it's legal. For example, property law is wildly tenant friendly if you actually push it. The explicit reason for this is that landlords have an illusion of power and almost always include unenforceable provisions.