Now that I got the attention, Why hasn't Pokemon been able to produce a succesful spinoff series unlike Mario which has a handful of them?

Mobileshit litteraly does not count and LGPE/PLA are spinoff as much as 3D Land/World are. Maybe the whole ''Pokemon begin the same for 20+ years'' argument wouldn't exist if they could produce something that isn't a oneoff spinoff entry
Also the current total number of 8 Deluxe is 48M copies.