Of course they say they won't do it. Because what could be done about it?
Everytime you visit an 18+ website, do they ask you to immediately email a copy of your driver's license to prove you're over 18 before letting you access said content?
When you create an account on youtube, does it ask you to verify you're over 13 by uploading a copy of your birth certificate?
Before you hit enter on your google search of 'naked Latinas' with safesearch off on the images tab, does Google do anything to confirm you're over 18?
And these are million/billion/trillion dollar corporations that could easily implement some sophisticated system if they so desire, but don't. If they aren't doing it, do you really expect a community of individuals to do so, or even a much smaller company like Square Enix?
The reality is, kids, teens, etc will always lie and get into stuff they shouldn't be, especially in this day and age. Trying to police such things would be a huge invasion of privacy bordering on 1984 territory, or be totally ineffective at their job. With how easy it is to get access to 18+ materials in literally 5 seconds with Google, it's entirely on the parents to be the dam that prevents their kids from seeing or experiencing things that the parent doesn't desire for them to be seeing or interacting with. Adults will be Adults, and adult activities will always occur in any online social setting, even if it's behind closed doors. If something arises, then the courts deal with it, but it's still equally a failure on the parent for letting their kid reach the point where something did arise.
When I look after my nephew, I have a remote connection window open on my computer that lets me monitor his website choices and make sure he's not up to anything suspicious. If he ever gets involved with an Adult, it's certainly not on my watch.
I also like how you say 'real' roleplay.
act out or perform the part of a person or character, for example as a technique in training or psychotherapy. - definition of roleplay, Google, 2021.
ERP seems like pretty real roleplay, acting out the role of another person or character, only in ways that you don't like; yet the character interactions are still as real as adventure RP. Or are you trying to imply that characters in fiction never do the dirty deed? Next you're gonna tell me Erotic Novels aren't real books compared to the grand fantasy adventures of Harry Potter or Lord of the rings, despite Erotica taking up an entire shelf at my local Barnes & Noble.