Arnold Schwarzenegger took the role of the Terminator very seriously (more on that in a while), but James Cameron loved the actor in Conan the Barbarian and noticed that part of what gave Schwarzenegger his presence in that film was how few lines he had (he only had 24 lines in that film).

So, he wanted the Terminator to speak even less. As a result, the Terminator only has 14 lines (16, if you count the lines where the Terminator speaks in another voice).