Generally speaking I think the allure of modern-day gachas is providing a near-premier gaming experience (like paid RPGs, open-world games, etc.) while being free-to-play, at the cost of slowly encouraging you to spend a lot of time and/or money to get better characters in order to actually keep up with the end-game content and/or PvP side of the game.

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.