There is one product missing from Candy Crush's shop, and its absence is the sharpest diagnostic in the whole shop.
They do not sell an Undo.
One step back. The single most obviously player-friendly boost a puzzle game could offer, trivially easy to build, and absent from every King game ever shipped.
Not an oversight. An Undo would repair exactly the thing the business model needs broken. The failures are the funnel.
What they do sell, and when
Look at what they do sell, and where. Candy Crush shows you three boosts before the level begins — before you have seen the board. Pyramid Solitaire offered five.
Think about what that timing assumes: you cannot possibly know which boost helps until you know the level. So the pre-level shop is not selling help. It is selling against your memory of failing the last attempt. And several of those items can only be bought before the level, never during it — which is precisely when the pressure and the need are highest.
Half the casual industry copied that screen without ever asking what it assumes.
Ask what the successful refuse to sell.
When you dissect a game, the question that reveals the most is not what it sells. Usually that question reveals a game's honour. Here it reveals the machine.