Why is Pokémon Adventures often playing the role of The Pokémon Company's neglected stepchild despite the great money-making potential for merch and to a lesser extent greater publicity?

Yes, Pokémon Adventures, better known as PokéSpe, did have some merch before, but it's basically a flash in the pan compared to what the games and Ash Ketchum got. Hell, Ash and the Team Rocket duo even got to be limited characters in Pokémon Masters EX, which is something that no PokéSpe character, or for that matter no character from a non-anime manga has ever had the privilege of getting, especially Yellow. Pokémon generates the lion's share of its revenue through merchandise, but if there is one aspect that constantly gets neglected merchandise-wise relative to the rest despite having been around for like almost the entirety of Pokémon's existence, it is PokéSpe. I just wish TPC would give PokéSpe some more love, at least on par with Horizons if not better. Hell, even including Yellow as another limited character in Pokémon Masters EX would be a decent start, let alone a brand new game featuring a brand new region that brings all the PokéDex Holders together like what Pasio did.