The problem is that you can only meaningfully pair program with programmers. The people involved in architexture/design meetings might not be programmers. The questions that arise when 2 programmers work might not be resolvable without involving the others.

I also think we're going to see a resurgence of either pair programming, or the buddy system where both engineers take responsibility for the prompting and review and each commit has 2 authors. I actually wrote a post on this subject on my blog yesterday, so I'm happy to see other people saying it too. I've worked on 2-engineer projects recently and it's been way smoother than larger projects. It's just so obvious that asynchronous review cycles are way too slow nowadays, and we're DDoSing our project leaders who have to take responsibility for engineering outcomes.

I’ve started pair programming with Claude and it’s been pretty fun. We make a plan together, I type the code and Claude reviews it. Then we switch.

You are exactly correct. As to why it’s unpopular, I believe it’s just that no one has given it a fair try. Once you have done it for at least 20 hours a week for a few weeks you will understand that typing is not and has never been the bottleneck in programming. If you have not tried it then you cannot have an opinion.