There wouldn't be the same problem (strictly looking at the UK age verification) if the UK Government had implemented a robust, secure system that online companies could use to verify the age of UK users. It would then be the UK Government's responsibility to secure and curate their citizens online presence. That would have been a shambolic mess that would have cost ten times estimates and never been implemented, but it would have been the right approach. The bulk of the cost to verify as an adult would occur once and could, in fact, be automatic.
Instead they threw the problem to each and every individual website, likely numbering in the hundreds of thousands, to implement their own solution increasing the cost by an ever-growing magnitude as new websites appear and old ones go away. This is blatantly anti-competitive, because large websites can afford to do this, while new or smaller websites or companies can't. Worse, having so many different third party age verification processes involved is going to be a scammers' paradise.
And I know people will say they don't trust the Government with that kind of information, but the Govt already has your passport, driving licence, National Insurance etc. etc. information. And your ISP has everything else.