Why Shuffle is the spot apps monetise
Getting stuck in Mahjong Solitaire isn't rare or a sign you played badly — it's a structural property of removing tiles in pairs from a fixed stack. Because it happens often, and because a player who's invested several minutes in a board doesn't want to abandon it, the moment right before a rescue is exactly when people are most willing to tolerate an ad or spend a coin. That's what makes Shuffle such an attractive place to put a paywall: it isn't optional the way a cosmetic unlock is, it's the thing standing between you and continuing to play.
The honest version costs the app almost nothing — reshuffling the remaining tiles is a cheap operation. Gating it is a business decision layered on top of a feature that could just be a free button, the same pattern as ad-gated hints in free Sudoku apps.