The problem, as I see it, is that there's generally no consequences for an employer (or anyone else) to put unenforceable clauses in contracts due to the concep

The problem, as I see it, is that there's generally no consequences for an employer (or anyone else) to put unenforceable clauses in contracts due to the concept of severability. It doesn't matter if parts of a contract are unenforceable, because the rest of it still is, so you may as well put as much bullshit in and hope nobody notices. In New Zealand, this is a big problem with rental contracts. Landlords and real estate agents will put a bunch of clauses that they know are unenforceable in the contract and hope you don't notice. Most people will think that they are enforceable though because they're in the contract. Usually I know better, but rather than bring it up with the agents at signing time, I've found the easiest thing to do is to just ignore the clauses, and when they try to enforce it, I tell them to pound sand.