It's a big deal for some players.
Let me ask you a question.
What significant advantage did WotC gain by changing the alignments? What is the purpose of it? How was it broken and needed to be fixed previously?
I don't doubt it's a big deal for some players, but I still have no idea why that should be more important that other considerations. Sometimes things change - gnomes were a big deal for some folks, too, but I don't think that's a pressing reason to leave them identical to their previous incarnations.
What advantages are there? By changing most traditionally good creatures to Unaligned, WotC removed the possibility that players will try and shoehorn or coerce a creature's behaviors based on its alignment.
I can also look straight at a creature's motivations and give it whatever motivations I wish without the need to modify the Alignment line or pretend it's not there.
I don't think something needs to be broken in order for it to change. I wouldn't have cared if metallic dragons were Good. As it stands, I prefer that they are Unaligned, and it's emphatically
not because WotC says it's better that way.
To use what some poster said on the WotC boards:
When you have good aligned creatures the exceptions who are evil (standard fantasy trope) are much more memorable. As karins Dad said, by being unaligned, golds are "Not really any different than many other dragons. Greedy. Conceited. Arrogant. Yawn."
Unaligned doesn't imply any of those, nor does it exclude lawful and/or good behaviors and goals.
It allows for them, sure, but it doesn't require them.
Unaligned <> Neutral
You can read it as, "No alignment specified" if you choose.
-O