Disalignment between TM / tutor

[Tracekun]

I noticed in Game, and in the wiki, a kind of paradox.

Some Pokémon can learn certain moves through TMs, but not through tutors.

For example  I ran into this problem while training a Sandslash, wanting to teach it the 'throat chop' move; for this exist an trainer at

Celadon City. but, one e there I discovered that it cannot learn that move.

Onli at that point, by looking again at the wiki I've noticed that anomaly. It's really disturbing, by the fact that the TM itself cannot be obtained in game, so why there is this disalignment?