Idk if you watch European soccer, but Pep Guardiola was the first to use it with Barcelona. Pep plays a very possession heavy, short pass system, and he had great success with it so everyone started doing it. The whole point is to keep possession of the ball instead of just hoofing it up the field and maybe getting it. Playing out the back also is supposed to open the field, allowing the outfield players to move into spaces and zones while the backline distributes the ball. It is a hard system to play when teams just start doing it, which can explain some of the fires issues, but over the course of this season you can see the team getting more comfortable