At a certain point, Valve boss Gabe Newell decided to change his approach to work. He reduced his involvement in the direct development of games.
Lead designer of Portal 2, Josh Weir, explained the reason for this decision in a conversation with Kiwi Talkz.
Gabe wanted to work on equal terms with the rest of the team, but his status constantly interfered with this:
He always wanted to be part of the team, but [Gabe is the boss], so it never really worked. People usually told him, "As you say," and he, on the contrary, said, "No, no, no, I want to be part of the team and come up with ideas together"
Gabe Newell realized the problem and, according to Josh, simply accepted the state of affairs and began to limit himself to general management and production functions:
It was difficult for other developers [to perceive Gabe as an equal], so I think there was a period when he stepped back a bit and said to himself, "Okay, I guess I just won't be able to interact with everyone in this way."