Why? To put it simply, there are 2 reasons. 1st is absolutely Game Freak Logic. Before you harp on me for answering this, I have a second reason. They didn't give Jump Kick to Cinderace because Jump Kick is a move that can't be selected in Gen 8. Additionally, Cinderace isn't the only Pokémon that would be left out in this group if Jump Kick could be learned in Gen. 8. This data comes comes from Gen. 7, the last Gen in which Jump Kick could be used. The other Pokemon like Cinderace are Blaziken, Meditite, Meficham, Scraggy, Scrafty, Hawlucha and Tsareena.
So, I believe that a combination of previous trends, Game Freak Logic and the fact that Jump Kick can't be used in Gen. 8 Led to Cinderace only being able to learn High Jump Kick.