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

https://paxtonsexpertop-ed.zenbloomer.com/posts/what-does-bar-mean-on-a-slot-machine

The number 7 is seen as lucky in slots and pop culture because it’s tied to long-standing symbols of fortune. In classic slot machines, hitting triple 7s (777) often means a big win