Because teens make up revolutions and warbands in societal regressions - they have nothing to loose and everything to gain, especially topheavy, elder centric societies like the west. Controll mechanisms are the stabilization agents preventing Hitler Youth, Red Guard runaways. And it works. Testrun completed. Now it can be gradually reversed and the useless elderly dispossessed off the holdings they cling too - if they pledge loyalty to the cooperate feudalist royalty.