ELI5: Why do firefighters need a contract?

This is really and truly an honest question. It's also not meant to be a knock against firefighters. More against the media and politicians who continually repeat this without explanation or justification.

It sure sounds bad, but if you step back: how many people actually have a contract? Firefighters have a job, they're paid, they have health insurance – all normal and reasonable things. They've even had pay raises. I'm pretty sure their pay and benefits could be adjusted without a contract. What else would a contract accomplish?

If it's such a big deal that firefighters don't have a contract, should we be equally concerned about every other worker out there without a contract?

Looking for a simple explanation 🙂