I'd also imagine you just have more communication overhead with more people. E.x. standups will take longer if you have twice as many people working half as mu

I'd also imagine you just have more communication overhead with more people. E.x. standups will take longer if you have twice as many people working half as much. And communication costs might even scale O(n^2) of people, not hours worked. I think that makes part time workers unattractive.