Smashboards

It's the same reason people play slot machines. Giving people rewarding prizes and random intervals conditions people to be more tempted to try again.

There's some psychologically that goes behind it and it's really manipulative and scummy. Most people are able to have to self control not to spend more then they can afford but some get caught by the hooks and blow money they don't have.

I enjoy playing gacha from time to time if it's reasonably set up. If I get enough enjoyment from it, I'll throw a little money their way.

It's fun to see what the game will give you sometimes. Honestly, I feel it's more rewarding to just wait and use free promo events or only occasionally spend some money on gachas, 'cause when you do eventually get something cool that way, it can be really exciting and fun.