Probably because not many distributors or dealers ordered rifles chambered for that cartridge or even knew Savage was going to have it available this year. Also, not being a hugely popular cartridge it's likely going to be one of those you have to have your dealer order from their distributor for you.

IMO the .280AI really has little more to offer performance-wise than the 7mm-08 (basically about 200fps), whereas the 7mm-08 offers several benefits the .280AI can't (fits a short action, less recoil, greater availability of factory ammo, etc.). The newer 28 Nosler isn't going to help the .280AI's popularity either. I'd be interested to hear how well the .280AI feeds from the magazine as having two rifles chambered for AI cartridges myself (one staggered-feed, one centerfeed) I can tell you from experience they don't always feed silky smooth due to the sharp shoulder angle and lack of body taper.