One of the problems with age ratings is that they’re from opposing cultural standards. Age appropriateness doesn’t mean much on a site where we’re all from different countries and social backgrounds.
Like, nudity is all-ages in some cultures and inherently seen as representing adult-centered sexuality in others.
The definition of adult varies by legal jurisdiction.
Any depiction of gun violence is considered too dangerous for young audiences in some places and inherently dangerous in others. Same for mentions of drugs.
In the US, where Itch.io is based, the entire site is restricted on many student computer devices (often the only regular way to access the internet for Americans under 18) not because it has “NSFW” games but because it has recreational games not reviewed by an educations company.
GameVolt.com is UK-based (and formed only about five years ago). The UK has the Games Rating Authority and laws that require age ratings and publishing laws that equate digital works to physical media. The US has entirely different laws, publishing history, and politics.
In case you meant the other Gamevolt: Gamevolt.net is an Egyptian site made for Arabic games. Many games that are popular on Itch.io straight-up would be illegal there.
In my opinion, more disclosures of content on game pages by the publishers. But required age ratings here would make the current policy shift and deindexing/reviews entirely disastrous for the site.