You say that like it's a bad thing. If my PCs aren't going to kick its ass at some point, why do I need stats for it?
Because you can do other things with it than "kick its ass".
Now the "standard" gold dragon is a lot like your standard "person", not good or evil, just doing its own thing . . . with inclinations towards being nice. But don't piss it off.
Except that this wasn't the reason for making metallics evil. No "grand fluff plan" to make D&D more interesting. If it would then the chromatics would be unaligned too. No, its just that in 4E everything which moves must be killable. Having something that moves and is good doesn't fit that. And so they break another tradition just to have more creatures to kill.
If they had higher reasons for it then I would have no problem with it. Its just this focus on "making things killable" and "if its not for fighting its not needed" that irks me.
And if you also want something more tangible, every time WotC breaks with a tradition they invalidate older edition fluff, be it fluff from monster books or fluff from campaign setting. Again, if they had good reasons for it, it would be ok. But their reasons is, imo, far from good. I would even say its rather bad.
Besides, why must every creature think and behave like a human? (Unless the creature is completely evil and can be killed on sight. Thats also perfectly acceptable. But having something inherently nice and compassionate? Thats a big no).