The reason why TPC stopped making Stadium-like games is because these games had much better visuals, animations and graphics compared to Gamefreak games.
The last game, PBR, was released during the time Gamefreak still making 2D games.
but now since X/Y, we see how much the graphics and battle animations are garbage looking. So, to not hurt the main games value and make people see them negatively, TPC won't make any stadium-like game ever, just for people to appreciate the Gamefreak 3D shitty visuals more.

It's psychology and marketing.