I got the 50k mileage offer in the mail in January for the Amex Gold Delta Skymiles card, but it required me to spend $3,000 within 3 months. The miles posted almost immediately after I hit my spending target.

Although the same number of points as the Premier Rewards card, the annual fee for this one is only $85, also waived for the first year.

I don't see a way to get this offer on their website. As far as why I was targeted, I didn't have a current relationship with Amex, but did have a closed corporate account.