In mid May, Remedy revealed that the music license for the Alan Wake games was expiring. This meant that the game would have to be removed from physical and online stores. As a means of saying goodbye, and giving hold-outs a way to finally take the plunge, Remedy had a sunset sale of 90% the game and its content on GOG and Steam. After the sale ended, the game could no longer be purchased. Everyone assumed that was the end of that.
Somehow, Alan Wake lives on, however. Over on Humble Bundle you can still purchase the title. The price is at its standard $30, though. So if price was your deciding factor, and you just happened to miss the sale, then you're out of luck on that front. Alan Wake earned a score of 83 on Metacritc, so $30 still sounds reasonable.
It's unknown why the title still exists on Humble Bundle. Maybe they have some loophole that allows them to still sell keys, or maybe someone at Humble HQ just forgot to take it off the digital shelf. Whatever the case, it's likely the title won't remain there for long, so it's best to grab it while you can, if you're still considering playing the horror classic.