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

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 its history as a positive symbol, like the classic 777 jackpot combination. It also relates to natural cycles, like the seven-day week, making it feel familiar and lucky