GREAT question. For one thing you’re not getting any job in mechanical engineering without a degree and an EIT, so that narrows the possibilities. Companies recruit at universities and this is the main pipeline into the industry. Connections are very important, so doing internships in summers during university gets your foot in the door. After you practice for ten years you get your PE and set up your practice either within a large company or independently. It is very likely that an ME can do their entire career without ever being subjected to the trick questions of some kid with six months of industry experience, like we pretend is normal for software developers.