The number 7 is seen as lucky in slots and pop culture because it 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 often symbolizes good fortune and completeness. For example, classic slot machines like those at MrQ use the 777 combo to represent a big win