If you commit to playing the gacha for an extended period of time, the system of:
- daily rewards that encourages you to play for a couple minutes each day to get enough currency to get good characters from the gacha
- newer characters being better than older ones (in visual design appeal and/or power-level)
- harder end-game content requiring better rosters of characters (or more grind)
- sales on the premium currency used to pull
- the ol' sunk-cost fallacy
all combine to encourage players to spend money over time
In this regard, the game in the post obviously does not have the scope of a game that actually costs money, and doesn't have the goal of getting you to spend money, but it does cover the grind and gacha part of pulling for different rarity characters and such.
Gacha is really just a monetization approach. The mechanics that accompany it are the real draw, and you can have card games, RPGs, tactics games, action games, etc.
In fact, I would describe this as an idle game, not a gacha game. In other words, a gacha-themed Cookie Clicker reskin. The emphasis is on the gacha, but in a real gacha game, rolling gacha occupies <1% of the playtime, and this doesn't adequately capture how the gacha model intersects with real gameplay mechanics.
It's really well done, and hilarious.