Some of us find the prospect of pairing with an unknown person in an unknown environment, and against the clock, to be very stressful.

Anecdote:

I've been interviewing recently and got through to the last round (of five...) with an interesting company. I knew the interview involved pairing, but I didn't expect: two people sitting behind me while I sat on a wobbly stool at a standing desk, trying to use a sticky wired mouse and a non-UK keyboard, and a very bright monitor (I normally use dark mode). They had a screen recorder running, and a radio was on in the next room.

I totally bombed it. I suspect just the two people behind me would have been enough though.

I've had a great career and very positive feedback from every employer. I would do absolutely terrible in this kind of interview.

I would find trying to solve such problems with known people in known environments to be somewhat stressful too.