It's important to realize that this isn't a game, it's 20 seconds of animation that looks like a game. There would be a lot more work designing levels or an algorithm to send enemies etc.

The actual game is designed to be as addictive as possible so you become a whale spending money on it. The advertising is designed to get you to download the game. Two different jobs.

Also, easier A/B testing and targeting if you can just advertise different games to different people but funnel them all to the same end game.

If the math worked out that people who saw the real game downloaded it and ended up paying more money, they would advertise the real game. Guess the math doesn't work.