Why were casinos levels so common in the early 2000s?

I was thinking over all the games I played when I was younger and realized that nearly all of them had at least one casino level. Does anybody know or have any theories as to why?

https://preview.redd.it/h7n6nl89wzp51.jpg?width=640&format=pjpg&auto=webp&s=cb303a23e8c26f184064bf71acd16675fa346aa0