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

https://wiki-saloon.win/index.php/How_Did_Casinos_Adopt_the_Meaning_of_Seven_Instead_of_Inventing_It%3F

The number 7 is seen as lucky in slots and pop culture because it’s tied to positive traditions and symbols. In classic slot machines, hitting 777 is a big win