Older members have been able to get the double points promotion and some of the significant fare sales that have been out there with the 20% off coupons.
There are always promos to get new customers and they don't always work out the best for existing customers. Sometimes that just doesn't seem fair, but the company can run the plan however they want to. I had several flights right before the double points promo started, and only got single credit for those. There are promos and sometimes you get to qualify and sometimes you don't.
Under the double points promo, you could get an award ticket for $750 in spend. Under the current system, now you would have to have $1000 in spend. Overall, the previous promo with double points should have been better for you than what's available now. If you didn't even get to 500 points during the double points promo, it's highly unlikely you're going to get to 1500 during single credit within 12 months to make it to an award ticket.