1 Arnold Schwarzenegger plays the lead role
Arnold Schwarzenegger, a global movie star, plays the lead role in the movies, that of a terminator T-800.
2 Time traveling is central to the plot
The plot revolves around time traveling individuals trying to reverse the future events by changing the past. This adds an element of novelty and mystery, which excites the viewers.
3 Unstoppable assassin robots disguised as humans
The Terminator is an assassin robot disguised as a human for easier infiltration. Just about anyone in the movie could suddenly change into a killer robot, and this fact keeps the audience engaged.
4 Memorable one-liners
Many of the one-liners have stuck with viewers for decades. 'I'll be back', 'Hasta la vista baby' and other phrases are popular even after 30 years.
5 Non-stop action scenes
The terminator movies are known for their non-stop action scenes which keep the audience engaged.
6 The franchise revitalized sci-fi genre
The first Terminator movie revitalized the sci-fi genre and made Arnold Schwarzenegger and director James Cameron famous names in Hollywood. The later movies capitalized on this success. (See Why Do Some People Like Horror Movies?)
7 Epic plot: The fate of many depends on a few brave ones
The story revolves around a handful of people trying to save mankind from a rogue AI Skynet that controls the robots and wants to end humanity's existence.
8 Central theme has similarities with real life
With the ever advancing technology, the audience is starting to question whether real life AIs will become a threat to humanity's existence one day. This increased the popularity of the movies, as their theme is more relevant today than ever before.
9 The Terminator model is eye-catching
The Terminator model, the metallic skeleton with red eyes, is eye-catching, scary and intriguing to many people. The iconic design made people find out about the movies even though they might not have been interested before.
10 Fans of the original movies increased popularity
Many fans of the original two Terminator movies praised the movies so much it increased the interest from common people to watch them. (See Why Animated Movies Are Popular?)