I think most countries have much stricter enforcement for gambling age limits, too. If you sell a kid a copy of GTA5 that's their parents problem, but if you allow kids into your casino it's your problem.
The problem is defining what falls under those laws. Companies sell trading card boxes with random contents. McDonalds had its Monopoly game. There are many more examples of things that are gambling with money, accessible to kids and still allowed in most countries.
Typically legal gambling has age limits by law, while the age recommendation for video games is just that, an recommendation. It isn't illegal for a 14 year old to play a game recommended to 18 year olds. Don't know how it works in the US specifically, at least how it works in other places.
I'm guessing the video games industry's attempt at self-regulating with PEGI and similar efforts actually paid off.
I can't speak for your country, but in Australia it's illegal to sell MA15+ rated material to an under 15, and R18+ material to an under 18. CS is MA15+.