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

https://meaninngs.com/what-does-the-number-7-mean-in-casino-games-and-popular-culture/

The number 7 is seen as lucky in slots and pop culture because it’s often linked to good fortune and completeness. For example, classic slot machines like those at MrQ use the 777 symbol to trigger big wins