The number 7 is seen as lucky because it appears often in slot machines, like...

https://damiensniceword.readspirex.com/posts/why-is-8-lucky-in-some-cultures-but-7-is-lucky-in-others

The number 7 is seen as lucky because it appears often in slot machines, like the classic 777 jackpot combo. It also connects to everyday cycles, like the seven-day week, giving it a sense of completeness