But yeah, it's not a single point, there are many points around that time that are pivotal, like Google acquiring DoubleClick in 2008. GMail taking off around the same time and increasingly making blocking more and more other mail servers. Google and Facebook adopting XMPP and then killing off federation in 2013 and 2015 once they had a lot of users. Apple introducing the iPhone, which resulted in phones becoming the main consumption device for many people, in a very locked-down ecosystem for users, where companies can extract all the analytics they can get their hands on.
Also, smartphones made people terminally online, which strengthened network effects and made it more attractive to make social media and games addictive. That doesn't work so well if you can only access the net at night on the family computer that is shared with four people. Even though I was a student when smartphones came around, I'd only check e-mail in the morning and maybe e-mail and socials in the evening.
But yes, I'm generally in the "it's the phones" camp of grumpy olds :)
Edit: Oh I just looked up the rollout schedule and it looks like it is more likely that I started my account in 2004. It might have taken it a year (at most) to become fully mainstream among my peers after that, so call it 2005 or 2006.
I think it's a bit fuzzy for "blogs". To me, it wasn't really until blogging became extremely accessible, that is without spinning up a website running software on your own servers, did I consider it "web 2.0". But then, yes, I agree that the explosion of blogs was fully part of that trend. (I was dismissive of this at the time, but in hindsight I think it's rad and I don't understand what my probably was.)
Definitely flickr is quintessential here!
Facebook didn't even exist 10 years before 2012 ..