Because you have to think upfront what are you going to say. You might me interrogated in front of everyone else about something that you are doing, and will have to come up with an answer on the spot.

This is obviously stressful, and psychologically pressures you to try to finish the task ASAP the day before, so that you can come up to the meeting and just say its done.

Which is the real actual benefit of the standup, and why managers keep doing it, despite they are obviously not needed and in most cases a waste of time.

The standup keeps everyone on their heels and feeling like their every breath is monitored and accounted for.

because they're unnecessary. I legitimately lose an hour a day due to them. I've started coming in late so I slide immediately into the daily standup because otherwise I fart around for the first 30-45 minutes until the standup starts.

There's just no deep work that can be done during that time, and that's every day.