So people are asking what a legal monopoly is, like they have never heard of USPS and the Patent Office.

Let me give you a definition:

Legal Monopolies are entities that legally have the sole power to do something in a sector. They emerge in one of two main ways either a company manages to get a patent on a product giving them exclusive control of the creation of that product OR the company is chartered by the government to run an industry making so that no other competition exists, like USPS, or Amtrak (both of these have grey areas and competition however in some form)