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

https://marcossmartchat.image-perth.org/why-are-there-seven-wonders-of-the-ancient-world-and-not-eight

The number 7 is seen as lucky in slots and pop culture because it often represents good fortune and completeness. For example, classic slot machines show triple 7s (777) as a winning combo