Remember - WotC can never satisfy every customer. So when a customer comes along who is disatisfied, it doesn't so much mean they aren't listening to you, as much as that they are listening to some else.
Bingo.
Recall first of all that the Player's Handbook Heroes line was canceled. WotC gave it a try and (I'm fairly sure) concluded that the market for PC minis is very limited. One DM can make good use of hundreds or even thousands of monster minis, but an entire gaming group may need only 4-6 PC minis for the whole length of a campaign. It's not that you can't make money selling PC minis, but they're not amenable to the DDM bulk-sales formula.
So PC minis--
all PC minis--are a niche item. DDM is aimed squarely at the Dungeon Master. The designers squeeze in PC minis where they can, but the big focus is always on the monsters. And dragonborn minis (along with goliaths, shardminds, genasi, and the rest of the wacky race brigade) are a niche within a niche.
Me, I've got very little use for the danged things. I'd be somewhat annoyed to see the wacky race brigade eating up a lot of Common/Uncommon slots that could have gone to filling in gaps in my monster lineup. I want those slots devoted to grunt skeletons, orcs, and the like--things that I'm going to need a
lot of and want to be able to get for cheap.
The secondary market exists for a reason. If you want a dragonborn mini, you can easily get one online from Oryan77 or Troll and Toad or something. It may cost a little more than you'd like, but you're shelling out that $6 to $8 so your DM doesn't have to blow hundreds on mooks*.
[size=-2]*Which is not to say your DM won't blow hundreds on mooks anyway... but she'll get a lot more for her money.[/size]