There's at least two key differences between something like Reddit or HN and Twitter. The Twitter platform is structured so that a large mass of people will "follow" a few influencers. It creates a really asymmetric power dynamic. On Reddit and HN, if you have interesting content, you can make the front page. On Twitter, your odds are much bigger if you're famous, and every comment a famous person makes is hugely amplified.

The second difference is that Reddit and HN are organized by topic. HN only has a single topic, but there's moderators to enforce that posts be somewhat on topic and retain a certain minimum of civility. Twitter is not organized like that. Even if you're just interested in programming, Twitter will try to get you to engage in political topics, and if you do engage, you might get responses from random people Twitter also pulled from other discussions who have very little context, and you'll get to exchange with this random set of people through responses that are limited in length. If a famous person happens to strongly disagree with you on Twitter, their hordes of fans will start to attack you.

So yes, all social media platforms have more active and influential users[0] , but no, these platforms are not all the same, and a lot of the difference is structural.

[0]: https://en.wikipedia.org/wiki/Pareto_principle