Because it was. Was probably this person's 10th interview of the day. They probably only need the simplest of infractions to weed someone out given the absurd volume of applications they receive.

> Because [arriving 15 minutes late to a 30-minute interview] was [nothing].

I'd expect over 95% of both interviewers and interviewees to say that arriving 15 minutes late to a 30-minute interview is very much not nothing; it's a serious breach of what is expected – on both sides of the interview.

If you show up late for an interview, no matter which side of the table you're on, you ought to apologize and, if you're more than a few minutes late, have a good explanation. To do anything less signals that you are an unreliable person. And, when you are representing a company, it makes the company look like it's run by people who don't even understand how to do something as simple as show up on time. It suggests that one of the company's unspoken core values is Dysfunction.

If I had shown up fifteen minutes late for the interview then they likely wouldn’t make an offer and they likely would have called it out during the interview. No one seems to call out companies when they do this shit.

They wouldn’t care if I had a really bad day beforehand, and they certainly wouldn’t assume that I had a good excuse for it.