Quanta is different because they could still hype A wakening with the rest of the Power Rangers after World. Unicorn only really has one lead mech so it might not be a very good move to debut the FA Unicorn now rather than later. Not saying it couldn't happen but it's more likely that we'll get something from AGE instead.
Popularity is irrelevant to secret units, they're not used to promote the game. And 3D was no more AGE's "game" than World was Unicorn's. We got like the first seven episodes, it's hardly even had a chance to shine yet.
Unicorn/00S2 didn't have anything special in World. They didn't have extra stages devoted to them, their rosters weren't particularly thorough or given special treatment compared to other series, it was just an ordinary debut. In the case of 3D, I would say they rushed to take advantage of the AGE hype at the expense of the game's content, even AGE's own, but then I would say the exact same thing about this game.