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

https://super-wiki.win/index.php/Why_Do_People_Pick_7_When_Asked_to_Choose_a_Number%3F

The number 7 is seen as lucky in slots and pop culture because it often appears in winning combinations like 777 on classic reels. Its charm also ties to the seven-day week, which feels complete and balanced