It creates a reliable interruption, such that if it happens you're likely to be distracted enough that it isn't even worth trying to get back into serious work for 45 minutes before you need to go home.
It's also late in the day, so any tasks that come up must pass a high bar to be actually remembered and resolved. A task must either be so urgent that it is worked on immediately (and then people will resent the standup for making them stay late) or so important that it can be remembered the next day. This means a whole bunch of simple-to-fix issues are probably being ignored, either by forgetting or just not being raised in the first place.
I'm not surprised that the meeting often doesn't happen. A better time for a standup is before lunch or earlier in the morning.