If I am right it is the opposite. It's because website owners block the UK IP addresses, as otherwise they could face criminal charges unless they buy an expensive compliance-as-a-service solution to check the age of all visitors and hire lawyers to craft "compliance policy" Ofcom can read. Otherwise you have a criminal liability.
Think it as a bit like GDPR but 1) much more expensive 2) with criminal liability 3) Makes even less sense than GDPR as it does nothing to prevent harm for minors 4) derimental for user experience and users.
"Funnily enough" the companies who lobbied for Online Safety Act, and former Ofcom employees, are now selling age verification check services and compliance services related to Online Safety Act. They have pretty good profit margins there, making even Google and Facebook look poor.
More here:
https://x.com/moo9000/status/1950866445186818209