> In the UK if you keep your mouth shut during an investigation, it may harm your defense. There is zero right against self-incrimination.

By "may harm your defence" what is meant is that Miranda was modified to inform people who are arrested that magistrates and juries are fully allowed to infer that you might be seeking to mislead the court if you didn't tell the police something significant that you later rely on as a defence in court. You're still allowed to do it, and they are allowed to conclude it is sketchy. That's the point of the modification.

Juries do and did this anyway.

The modified Miranda doesn't say you have no right against self-incrimination; it now warns you that if something is crucial to your defence it might be in your interest to mention it so the jury doesn't think you are trying to shine them on.

It's important to understand that this happens in the context of a country that does not have a plea bargaining mechanism. Cases go to court if it is in the public interest that they do (and the police don't decide this). But you can still no-comment your way through an interview and you aren't going to be bullied by a prosecutor into accepting a plea deal.