To be fair, working in a theater throughout high school, I can tell you that most of those emergency exits are not rigged with alarms. In fact, in cases of extremely crowded theaters, we would often times (at the end of the movie), open up those exits for people to go out at the end of the movie to make it easier (and less congested) once the film ends for people to get to their car.
This is working in theaters in three different states, with two different companies. Things may have changed since then (since this was a while ago), but I don't find it shocking at all that there wasn't an alarm on those doors since they aren't technically your traditional "Emergency Exits" a lot of the times.