app marketing mechanism
What’s the ROI of iMessage Stickers?

This. I have installed at least 3 apps due to their sticker pack offerings, adventure time TAKE MY MONEY.

I was wondering why a few apps had obv just chucked in most or all their graphic assets as stickers, then realised the first time a game someone sent me to play a turn, asked for $4 or something. Very clever maybe unintended but great marketing/ discovery.