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

https://tysonsinterestingperspectives.cloudhinter.com/posts/is-it-really-seven-years-of-bad-luck-if-you-break-a-mirror

The number 7 is seen as lucky in slots and pop culture because it's tied to classic symbols like the 777 jackpot combination on reels. It also relates to the seven-day week, a familiar cycle