(didn't want to derail the thread so I'm replying here)
Apparently, it's because they want each game to be different. Which is fine, but (like everyone else) it just makes me miss the old style. Super Paper Mario was an awesome game, but it didn't live up to the originals. Sticker Star promised to bring the series back to its roots, but ultimately failed. For one thing, you couldn't gain EXP from battles which made fighting pointless. But the reason I didn't buy the game was the story, or lack thereof. I just hope the next Paper Mario game follows the formula that made Paper Mario popular in the first place.