There was a time when large airplanes all had four engines and three pilots. Taking out the third seat made economic and operational sense, as two pilots with a limited degree of automation were enough. But they had to work at it.
Then it got easier as GPS eased the navigation chore, engines got larger and more reliable, and there were fewer of them to manage.
Now computers fly the airplanes and pilots control the computers. It does not take two of them to do this. One could manage the same way two did when they took out the third seat. That is not the problem. The problem is bad days. We all have them. You don’t want to be all alone up there when you are having yours, do you? Or in the back when it is someone else’s turn.