I’ll just avoid sites and services that require this.

It's not the site wanting to do it. It's a requirement from Parliament in the UK.

https://en.wikipedia.org/wiki/Online_Safety_Act_2023

The Online Safety Act 2023[1][2][3] (c. 50) is an Act of the Parliament of the United Kingdom to regulate online content. It was passed on 26 October 2023 and gives the relevant Secretary of State the power to designate, suppress, and record a wide range of online content that is deemed "illegal" or "harmful to children".[4][5]

The Act creates a new duty of care for online platforms, requiring them to take action against illegal content, or legal content that could be "harmful" to children where children are likely to access it. Platforms failing this duty would be liable to fines of up to £18 million or 10% of their annual turnover, whichever is higher. It also empowers Ofcom to block access to particular websites. It obliges large social media platforms not to remove, and to preserve access to, journalistic or "democratically important" content such as user comments on political parties and issues.

I mean, you don't have to go there if you want, but it's probably Parliament you want to be irritated with, not websites following British laws.