Very interesting question. As an Italian (specifying this because it probably changes what and when things happened), I remember this transition started to happen in 2010 mainly because of Facebook.

It’s difficult to say why we decided to go with real names on that platform when there were already other similar ones (netlog was super popular here), where most people were mostly semi-anonimous (real pictures, fake names). I totally agree with another comment which said we started to realize internet was not that dangerous or bad, which probably made this happen, combined with the fact that Facebook explicitly asks for your real name.
Back then, I feel there was also much less attention to privacy on the internet (or maybe it’s just because I was a teenager), and it felt super exciting to engage with every new platform or website.

I’ve been seeing a lot of posts about Threads privacy policy lately, where people seem genuinely shocked about it. I think it’s good to raise awareness about how much data you’re selling to Facebook company if you choose to use Threads, but I think it’s also good to remind people (as the article does) that this happens also when you use Instagram or Facebook itself. Ditch Meta