I find it odd that none of these guys learn moves based on their material of choice. Timburr doesn't learn Wood Hammer, Conkeldurr doesn't learn Sand Tomb, Gurdurr doesn't learn... I dunno fuckin' Metal Burst or some shit.
My understanding is that Wood Hammer is not 'using a piece of wood as a hammer'. It's supposed to involve charging into the target with a hard, plant body and hitting it downward like a hammer (the wood is probably chosen as it is plant-related and strong).
Guys we're overlooking the more obvious choice for Timburr to learn: Branch Poke.
Steel Beam, duh.
(Yeah, I know, I know ...)
Actually a Steel-type move they can all reasonably learn would be Heavy Slam. Though honestly they'd probably do better with Gyro Ball.
But yeah, as
Worldie noted, they're probably just avoiding giving it an elemental move that wouldn't make sense for its evolutions (unlike Komala and Mimikyu who always have their log/stick so get Wood Hammer). So no Grass at least. As I said Heavy Slam or Gyro Ball I think is reasonable. And with Conkeldurr being the final evo maybe they could give it specifically a Rock-type move like... well actually it already gets Stone Edge and Rock Slide, so does it need another Rock-type move?
If the issue is that they don't get a move where they swing their object of choice, honestly that sounds more like something that could be made into a Signature Move for it. Make it Fighting-type but, just for fun, depending on stage its at it gets a different secondary effect: Timburr does super effect damage against Water & Ground-types; Gurdurr ignores resistances & immunities, and Conkeludurr ignores all Abilities and breaks through Protect & all its variants (& maybe to have also have another secondary effect that's consistent between all of them like a chance to flinch).
Despite the fact the move involves the user hitting the target with its own item, something that could be done via telekinesis, the only non-Ghost-type, Psychic-type Pokémon that can learn the move is Mew.
In addition to what has been said justifying the inclusive nature of the move, this got me curious: Mew is the only non-Ghost Type that learns it (cause Mews gimmick is it can learn every TM & Tutor), but are there any Ghost-types in SwSh that doesn't learn it?
Turns out, there 11, or 6 families if you wanted to group them up: Drifloon family, Mimikyu, Honedge family, Blacephalon, Dreepy family, & Spectrier. Not sure why they were excluded, it's very odd in some of their cases as the Drifloon family and Honedge family are already possessed objects. Mimikyu may not be possessing something but its obviously manipulating its disguise which included a stick that its using as a tail.
There's already like a million "slash" moves (Slash, Night Slash, Psycho Cut, Cut, Fury Cutter, X-Scissor come to mind). Adding a "steel type slash" probably felt redundant, expecially when a relatively widely distributed steel type attack already exists (Iron Head)
Eh, if it still looks like there would be some Pokemon who has metal blades part of their design that they use for attacking (Scyther family, Kabutops, Skarmory, Empoleon, Excadrill, Escavalie, Pawniard family, Durant, Cobalion, Honedge family, Alolan Sandshrew family, Kartana, Corviknight, Galarian Meowth family, Zacian) I don't see what's the foul of making a Steel-type version of Leaf Blade and call it a day. Like, there's a lot of punching moves, there's even an Ability that works with it, yet no one is saying there's too many of those.
Or they could get creative, like maybe have a Steel-type version of Thrash which implies rapid slashing (Slicing Storm) or copy of Triple Kick that implies a succession of strong sword swings (Slice Dice).
They're pretty clearly taking liberties with what constitutes a horn when assigning the move to Pokémon but the Japanese name really is "Smart Horn" in katakana.
It's a bit of an odd move in general; not sure why piercing attack with a horn that always hits is Steel-type. Maybe it's using the horn as a radar to home in on opponents?
Honestly I'm not even sure why they made Smart Strike in the first place (or why the English translators changed it from "Smart Horn"). And it doesn't make sense Kartana learns it. It feels like it may have started out as a Steel-type cutting move wanting to give something to Kartana (it's essentially a Steel-type Aerial Ace which in Japan is named after a sword technique), but out of the blue someone went "hey, if we made it a horn attack we can spread it to a wider range of Pokemon!", and did that but kept it on Kartana anyway without much justification besides it was originally designed for it.