Small forums run as hobby projects need to require little-to-no investment of time and money, or the ROI quickly goes negative and they just shut down instead.
A little while back there was the story [0] of a Mastodon admin who hated CloudFlare and its centralized protection, but found that he had no choice but to sign up for it anyway because a disgruntled user kept launching DDoS attacks and he had no other way to keep his instance online. A bunch of people here and elsewhere kept unhelpfully replying that, “you don’t need CloudFlare, you could just do [incredibly convoluted and time-consuming solution] instead”, and all of those people were missing the point: CloudFlare is “set it and forget it”, which is a non-negotiable requirement for anything which is run as a hobby instead of a full-time job.
It’s the same with this UK law: yes, you could spend weeks of your life learning the intricacies of laws in some other country, or you could just block them and be done with it. Businesses which might need revenue from UK users will do the former, but if I’m running a site out of my own time and money, I’ll do the latter. And I don’t want hobby sites to have to disappear: the Internet is commercialized enough as it is, and regulating passion projects out of existence would kill the last remaining independent scraps.
[0]: https://news.ycombinator.com/item?id=21719793