You probably have seen those ads where the player's character shoots at enemies and objects on a 2D road. The player deliberately makes incorrect choices to entice you to play the game, but the ad is fake and the game is a pay-to-play base-building a la Clash of Clans.

So what are those ads? If I were to guess, they are games thrown together in 15 minutes in a game engine like Unity just to make the ad. Would I be correct?