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

https://fernandosmastercolumns.swiftnestly.com/posts/why-is-seven-easy-to-recognize-on-a-spinning-reel

The number 7 is seen as lucky in slots and pop culture because it often represents good fortune and completeness. In classic slot machines, hitting triple 7s (777) usually means a big win