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

https://wiki-canyon.win/index.php/Where_Did_the_Lucky_7_Idea_Come_From%3F

The number 7 is seen as lucky in slots and pop culture because it often appears as a winning symbol, like the classic 777 jackpot on slot machines. It also feels familiar since we have a seven-day week