I'll defend the idea that it was obvious. (Although, it wasn't obvious to me until someone pointed it out, so maybe that's not obvious.)
If you watch this video[0], you'll see in the first frame that there is a clear boundary between learning rates that converge or not. Ignoring this paper for a moment, what if we zoom in really really close to that boundary? There are two possibilities, either (1) the boundary is perfectly sharp no matter how closely we inspect it, or (2) it is a little bit fuzzy. Of those two possibilities, the perfectly sharp boundary would be more surprising.
If you watch this video[0], you'll see in the first frame that there is a clear boundary between learning rates that converge or not. Ignoring this paper for a moment, what if we zoom in really really close to that boundary? There are two possibilities, either (1) the boundary is perfectly sharp no matter how closely we inspect it, or (2) it is a little bit fuzzy. Of those two possibilities, the perfectly sharp boundary would be more surprising.
[0]: https://x.com/jaschasd/status/1756930242965606582