Adding an emo option is surely the best way to go.
What's the warlock then? Chopped liver? There's more than enough emo in that to feed your Black Parade fantasies on for some time. Oh the angst, where is my scarf and black-rimmed glasses? I can't see past this fringe to slit my wrists.
Let's own up, horns look cool in promotional artwork. That's the real reason. Or some survey revealed that +2 to dex and int was more popular than +2 to wis and cha, because I'm sure 3E players had flavour in mind when powerbuilding their PCs.
Sorry, just a bit cynical about it all...and I picked the tiefling as the "new drow" and all, but note that the drow wasn't in the core. Maybe it should have been. Drow and elf, tiefling and aasimar - remove "eladrin" and dragonborn and there's a nice symmetry there, with less arbitrary D&Disms, because both sides of the coin are present, giving balanced flavour to match that balanced crunch which is oh-so-important.
For bonus points, rename tiefling and aasimar to demonblood and angelblood or something, so they're self-explanatory. Or use proper english, like cambion. Words that "survive" in english are generally better than anything you care to fabricate, because they've passed a usability test. They sound proper, unlike "eladrin" for instance.
Overall a much better core than what we're getting, IMO, and I've only spent the time typing here in thinking about it. That probably shows, but it seems no less arbitrary than what we're being presented with, surveys or not.
Speaking of surveys, are dragonborn born out of the newbie players who know nothing about the game saying, "Dungeons and Dragons? Okay, I want to be a dragon!" Because you're not really giving them that with dragonborn. Give them the real thing, say I, give them a playable dragon. Permutate them into a playable PC. It would be genuinely less intrusive than dragonborn are, and dilute the game's dragons less than this does. Water water everywhere but not a drop to drink....Draconic everything but the dragons themselves.
The only other reason why "survey says dragon-races are in" is probably for powergaming reasons (i.e. 3E half-dragon powers and stat gains), or related to that marketing radar blip that books with "dragon" in the title sell more. Both bad reasons to compromise the IP in the core IMO.