To understand this, it helps to know some basic things about flight aerodynamics and stability. Early planes were highly stable, and so are airliners. To dart about quickly requires special advanced brains and reflexes, which later birds and pterosaurs had, but early ones did not. The analogy in planes would be fighter planes, which need such fast reactions that the details are worked out by computer, with the pilot indicating where to go. It requires more brains to control unstable flight than it does stable flight.