I'm not sure that is immature at all.
It is more like, you already HAVE a thing, enjoy that thing, then someone takes that thing from you, say a toy. Then you are told "it's fine we are giving you a newer toy" and you go...well....I really liked the other one you took from me, but alright.
Then two years later you gave up hoping for that toy after years of glaring at your parents for taking it away, then they finally go "Hey look, here is that thing I promised you two years ago!" and you would just look at them funny.
Sure some people might go "awesome, new toy", but some of us still remember the one that was pointlessly taken away with a complete b.s. reason ("too many constraints with the current lore"), then given nothing almost for 2 years straight.
It's okay for you to be cool with that, but don't call someone immature for not having the same reaction as you.