The number 7 is seen as lucky in slots and pop culture partly because it...

https://meaninngs.com/what-does-the-number-7-mean-in-casino-games-and-popular-culture/

The number 7 is seen as lucky in slots and pop culture partly because it appears in classic reel symbols like 777, which often means a jackpot. Its positive vibe connects to things like the seven-day week, making it feel familiar and lucky to many players