The problem with the move is that it doesn't fit them.Very sad that Garchomp does not get a new physical Ground STAB however, especially in the absence of both Dig and Earthquake. No High Horsepower or Headlong Rush? Sad. It's stuck with either the weak Bulldoze or using Earth Power coming off its lower (and relatively middling) Special Attack, unless it learns High Horsepower through other means. Even Hippowdon is capable of learning High Horsepower naturally, and same with Rhyperior and Mamoswine, why didn't they do the same with Garchomp?
Oh wait...Gliscor doesn't have a good Ground STAB in this game at all dammit. I seriously do hope High Horsepower is tutorable in some form because Gliscor and Garchomp really need it with both EQ and Dig gone.
The move (which again has nothing to do with horses or kicking and is a reference to actual horsepower) would basically imply the pokemon to ram into the enemy with all their weight, and is thus learned mostly by massive and heavy pokemon and well, horses cause of the pun. (and obviously, their pre-evos)
Examples:
Unfortunately this isn't something that would remotely fit with Gligar/Gliscor, who barely weight 42 kg and are pretty slim and agile enough to float, so aren't exactly ramming into anyone.
Garchomp is a more interesting case since it's definitely massive and heavy enough to use the move, however I assume the reason for it not learning it is that it's described as an agile and fast pokemon (tecnically fast enough to be capable of flying at mach speed) so I think it doesn't get it because of it not thematically fitting. (Ironically I think it'd fit *mega* garchomp very well).
So I'm afraid as far as this specific game goes, they are kinda stuck with not having a proper ground stab.
The good news is, since this game has no PvP, most likely this doesn't matter and the game will be a joke to beat anyway cause it's Pokemon.