The term "gacha" comes from "gachapon" a type of vending machine in Japan that dispenses capsule toys. These machines, popular for their element of surprise, have been around since the 1960s. The key characteristic  is randomness; you insert money but don't know exactlywhat you'll get

These games often employ psychological principles similar to gambling, The randomness and unpredictability of gacha pulls (akin to slot machines) can trigger a dopamine release, creating a sense of excitement and anticipation.

Searchcaster