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

https://www.bookmark-jungle.win/the-number-7-is-seen-as-lucky-because-of-its-long-standing-cultural

The number 7 is seen as lucky in slots and pop culture because it shows up often in old-school reels, like the classic 777 jackpot on machines. It also feels familiar and positive since we have a seven-day week