Sad to say it but there are a few "good" reasons. I have good in quotes for a reason. Of course, given the circumstances and the fact that she had two small children with her lead me to think he was just being a p---k.
1. The residents of the building are PITAs have nothing better to do and will complain/report the doorman for letting non-guests loiter in the lobby. (We have a few of those here)
2. The management company and/or board are "by the book" types and come down on all rule infractions so all staff must make bad choices in order to keep their jobs.
3. We just got hit with a scam that has been going on in high rises around here forever. Someone will come in and claim to have an interview/appointment with the building manager. While the doorman is calling the manager the "interviewee" will find a carpet to trip on or an invisible spot to slip on and suddenly he is "hurt" and in need of an ambulance. In our case, the front desk is monitored by our security system so the guy had no chance here.
There are a few others but you get the picture.
DM