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

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 symbolizes good fortune. Classic slot machines like those at MrQ feature the triple 7 or "777" combo, which is a winning line