LogFAQs > #942138926

Sticker Star is the way it is because basically the overall series head, Kensuke Tanabe, revealed in an interview that among the many games he was a producer for at Nintendo one was Freshly-Picked Tingles Rosy Rupeeland for the DS. Tanabe was enamored with how Tingle started and ended the game at the same strength level, instead using money to solve his problems, and that is why Sticker Star used the battle system it does.

As for why they haven't made a game like the first two it's because Japan is apparently not fond of Thousand Year Door and all the Club Nintendo surveys they got about Super Paper Mario said that fans overwhelmingly despised the story.