Marketing. Just cheesy marketing for unknowledgeable rich people who like new trends.
Not entirely. And the proper pronounciations are "JAG-U-WAR" and "coo-pay".
Enough with the jokes. A coupe is not necessarily a 2-door and a sedan is not necessarily a 4-door, although most of the time they are.
A coupe (the automotive definition as adopted from carriages) will have less head room in the rear seat than the standard model, so many 2-door variants of 4-door cars fit into this category and are therefore 2-door coupes. The latest Mercedes-Benz CLS and Volkswagen Passat CC are coupes, according to this definition.
If the 2-door version of a 4-door model has similar rear seat room, the 2-door is called a 2-door sedan.
Let's not get into the misuse of terms like Brougham, Landau, or Phaeton at this point though.