The number 7 is seen as lucky in slots and pop culture because it often signals...
https://zanesnewthoughtss.evergrovio.com/posts/why-does-seven-show-up-in-calendars-religion-and-games-at-the-same-time
The number 7 is seen as lucky in slots and pop culture because it often signals a big win, like hitting 777 on a classic slot machine reel