Why don't engineers have protected titles like MD's (doctors do)?

More and more tradesmen and even manual laborers are beginning to refer to themselves as engineers. I've heard diswashers calling themselves "solutions engineer", garbage men calling themselves "sanitations engineer", and automechanics calling themselves "automotive engineers". Real engineers who've done at least 4 years of undergrad and taken a differential equations class are beneficial to society and actually make a big difference, so don't engineers deserve protected titles much like doctors do? If you call yourself a doctor, you could see many years behind bars. But any average joe can call themselves an engineer. It must be frustrating for real engineers whenever they tell people they are an engineer but are thought of as some mechanic or electrician.