Historically, people in areas all over the world have ridden Tauros, but the practice is said to have started in Alola.
-Pokedex entry in Pokemon Sun
The Tauros of Galar are volatile in nature, and they won't allow people to ride on their backs.
- Pokedex entry in Pokemon Shield
…and is featured in Pixelmon as the silhouette for Mount Boost.
Gogoat was one of the first Pokemon that the player could use as a mount in X/Y. People all over the Paldea region ride Cyclizar (and the player rides its future/ancient relatives).
It only makes sense for these 3 (and Miraidon/Koraidon, whenever they’re implemented) to receive inherent access to Mount Boost.