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

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 because it often signals big wins, like hitting 777 on classic slot machines. Its luck ties back to the seven-day week, symbolizing completeness