I was checking out Hyper Beam's availability and found out a very odd little thing about it. So, conceptually, Hyper Beam is meant to be this super strong attack that's given to fully-evolved Pokémon, and that rule is generally well followed throughout the series, if a Pokémon is fully evolved, there's a very big chance that it might be able to learn Hyper Beam in some sort of way, mostly through a TM.
There are several exceptions to this "fully evolved" rule, although most of them are very understandable. The first of which is Pokémon who were fully evolved at some point in the series but aren't anymore, such as Lickitung, Porygon or Chansey. This exception explains itself. The second exception is a bit weirder, Pokémon that were never fully evolved at any point. This makes more sense when you analyse each case individually, with Hyper Beam being given to these Pokémon generally due to it making thematic sense. This exception is applied to several unevolved pseudo-legendaries (which are conceptually meant to be stronger, exceptional Pokémon), Trapinch (very similar idea to those), Remoraid, Klink (both being Pokémon sorta related to "beam" moves and that kinda stuff, so it makes sense from a thematic standpoint) and Amaura (which is also like that, and also they really wanted to showcase Refrigerate with it).
Here's the thing about all the Pokémon from this second exception: all Pokémon that were always considered unevolved and still can learn Hyper Beam will learn it through level up, it was a move deliberately given to their natural learnsets individually, so them being able to learn it through a TM only makes sense. But there's a single exception to this:
Nuzleaf.
Nuzleaf was never considered a fully evolved Pokémon, and it still being able to learn Hyper Beam anyways makes so little thematic sense that they didn't even give the move for it to learn naturally through leveling up. It's the only Pokémon from this second exception that only learns it through TM, and that's been the case with it ever since its introduction in Gen 3. This doesn't even happen to its counterpart Lombre, so it is the only case I noticed that had this bizarre quirk in its learnset, and I cannot think of any explanations for why this happens.