If you are genuinely asking about the differences, the fact that greeding a GCD is bad is easier to learn for newer players, while tanks having damage stances and tank stances, healers having the HW cleric stance is way harder to utilise in comparison; for example if a player greeds a GCD without knowing it would wipe the party, others will tell them to not greed and assume the player listen, they simply don't greed and follow the others, a simple choice between to greed or not to greed, but the same thing cannot be said to stances unless you could teach a tank in real time when you switch between stances or when to use enmity combo.
At the end of the day, tanks and healers having stances made those roles had more responsibility hence less players were willing to pick up those roles, SE had to do something to remove some of the illusion of choice that made the roles less approachable to reduce the DPS queue time, as a result, here we are!
(for reference I only started the game as healer from early SB and didn't pick up a tank job until near ShB so maybe someone else have better ideas)