Retpolines certainly existed in November, perhaps before. But it's somewhat harder to modify compiler+kernel than shipping microcode you get from Intel and mod

Retpolines certainly existed in November, perhaps before. But it's somewhat harder to modify compiler+kernel than shipping microcode you get from Intel and modifying the kernel to adopt a (no matter how ill-designed) new CPU feature. Also, it's not easy to make sure that retpolines cover all the corner cases. There was little time. Intel engineers are a nice and cool bunch. It's not their fault.