Legally speaking, that is often the case. Many states require a noncompete to have a “legitimate business reason”, and proprietary knowledge is the most common legitimate reason used.
I suspect judges in most states would invalidate a noncompete for a sandwich shop worker.
The legal purpose of these clauses is to keep high paid workers from stealing customer lists or business secrets. The legal system does tend to frown on them being used for rank and file.
Many employers just use them as an empty threat to manipulate people, because they know few people are going to hire a lawyer over it.
I mean, even from a practical perspective, noncompetes are pretty weak unless the employee is the kind of person who would make the news when they join a new company. You can always leave a company and tell them nothing about where you’re going. A subway franchise ain’t gonna hire some PI to figure out where a former front-line employee got a new job.