You have to realize that the developers of these games can't enforce anything themselves. What are they going to screen everyone who buys and game and see if they have a valid drivers license or photo ID to see how old they officially are. It has always been the responsibility of the parents and there are some parents that use video games as a time occupier so that they do not have to deal with their kids that they know are immature and need a good ass beating.
Which is why spoiled bratty kids grow up into spoiled bitchy adults and then the cycle continues.