Which, perhaps ironically, is a small plot hole in the movie. "Wardialing" is not possible with a coupler - since the computer has no ability to hang up, or dial. When using a coupler, you have to dial manually.

Could you not run a relay from thr parallel port and pulse dial?

Yeah, you could. But there’s no pulse dialing depicted in the movie.

I was wondering about that, but I didn't update my post. Was there an acoustic hang-up signal? I've forgotten.

Regardless, the 1200 baud modem, in addition to feeling like it was "keeping up" with the user, also made connecting more convenient.