>>50569354Joke answer: Pokemon are converted to data and you can install the TM into them to slightly alter their bodies and make them able to use moves. Not all TM's are compatible with all Pokemon because the change could be too extreme. Like giving a quadruped punching moves, or giving an ice type fire moves. The company that manufactured TM's in Poke-Japan (Kanto, Johto, Hoenn, Sinnoh) included DRM that made the TM's only usable once, but in ORAS, they got bought out by a company from one of the other regions and started making their TM's unlimited use. Galar's TM company sells both forms of TM's, but insists that the single-use ones are different or that it's unavoidable.
Serious, canonical answer: Tiny instructions on how to use moves are written on the TM and the Pokemon shrinks down to read them. When the Pokemon grows back to normal size, it's still standing on top of the TM and accidentally breaks it. They're unlimited use now because TM manufacturers just made them more durable.
