There are probably many reasons, but I think there are two ones worth mentioning (aside from money, which everyone else has mentioned so I won't bother).

First, pretty much everyone is online now. The real greybeards of the internet talk about Eternal September which is when the internet first began to reach a larger audience in the early 90s. IMO the same thing happened (on a much bigger scale) with the advent of smartphones. The difference in scale between mid 2000s and now is difficult to imagine. And I just don't think you can have a cohesive culture across such a vast set of people.

The second (related) reason is that you are a lot older now than you were back then. Most of us who grew up in that period just don't have the same interest in memes as we used to. I presume younger people do have their own memes but (i) they are less likely to pop up on the websites I browse, (ii) when they do, they don't interest me, and (iii) because there is so much more content out there now, each individual meme is probably shorter lived.