Here's why it's often just called "1701":
* NCC-1701 is the official registry number of the starship.
* In Star Trek, the registry number is a unique identifier for each ship, similar to a license plate.
* Fans often use the registry number as a shorthand for referring to the ship.
So, "Star Trek 1701" is essentially a nickname for the original USS Enterprise, making it clear which ship people are talking about, even if they don't mention its full name.