I believe they intended it to be forwarded via the "tell a friend" link to test the power of viral marketing. Then it got out of control due to FT, Fat Wallet, etc. They either pulled the plug or the preset limit was hit. Note that they already had the graphic of the foxy FA ready saying the Dash to the Gate will return, so I think they hit the limit.

They created a huge buzz and will launch it again prominently featured on the website and award fewer miles on the 2nd go around.

FWIW, I played for my account and my wife's. I played for my two boys and signed them up for skymiles. My wife's long dormant account with 7000 miles in it which never expire - I am going to at long last get a copy of our marriage license and update her name to her married name. So for 40K miles, Delta has in my family got two new SM members and reactivated a long dormant account - now that the whole family are SM members I would consider a holiday flight on Delta - in the past it would only have been on US UA or NW as those are the only airlines we were all FF members on. At a bare minimum, we will all four engage in partner activity once every 3 years to keep our miles alive.

My guess is they may get quite a few Amex cards signed up for out of this - and then sell a lot of miles to Amex. Maybe Amex underwrote this with the miles they pre-bought from DL.