The Fediverse by design prevents this, while the internet of the old age had little if any guardrails against this specially since the platforms never really federated with another.

Did forum sites even federate? One forum sites would be dead and the next would have more activity. But what if the other forum with less activity was the one you wanted to use? The old internet was a good start but there's a reason why it's dominated by Instagram and Facebook, while email, you can use mostly any provider and not feel like you're left out.