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

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 of the classic "777" jackpot symbol, which players associate with big wins. It also connects to everyday life, like the seven-day week, making it feel familiar and special