The number 7 is seen as lucky in slots and pop culture because it’s tied to...

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’s tied to positive things like the seven-day week, symbolizing completion. Classic slot machines often show triple 7s (777) as a jackpot symbol