[rozab]

These techniques aren't tightly restricted trade secrets or anything. Companies talk very openly about their techniques at conferences. They see engagement (or less charitably, addiction) as a laudable goal and I can sympathize with that - there are lots of activities that people find 'addicting' which aren't viewed negatively by society (running, knitting, sudoku, baking, etc).

Anyhow, here's a talk on engagement based matchmaking in Halo 5: https://youtu.be/0FoG4Jtpebs